The semiconductor element includes an oxide semiconductor layer on an insulating surface; a source electrode layer and a drain electrode layer over the oxide semiconductor layer; a gate insulating layer over the oxide semiconductor layer, the source electrode layer, and the drain electrode layer; and a gate electrode layer over the gate insulating layer. The source electrode layer and the drain electrode layer have sidewalls which are in contact with a top surface of the oxide semiconductor layer.
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10. A semiconductor element comprising:
a semiconductor layer over an insulating surface;
a source electrode layer and a drain electrode layer on the semiconductor layer;
sidewalls provided in direct contact with a side surface of the source electrode layer and a side surface of the drain electrode layer;
a gate insulating layer over the semiconductor layer, the sidewalls, the source electrode layer, and the drain electrode layer; and
a gate electrode layer on the gate insulating layer,
wherein the sidewalls are provided between the gate insulating layer and the source electrode layer and the drain electrode layer, and
wherein the sidewalls and the gate electrode layer overlap at least partly with each other.
1. A method for manufacturing a semiconductor element, comprising the steps of:
forming a semiconductor layer over an insulating surface;
forming a source electrode layer and a drain electrode layer on the semiconductor layer;
forming a film serving as sidewalls on the semiconductor layer, the source electrode layer, and the drain electrode layer;
forming sidewalls by etching the film serving as the sidewalls, the sidewalls being in direct contact with a side surface of the source electrode layer and a side surface of the drain electrode layer;
forming a gate insulating layer over the semiconductor layer, the source electrode layer, the drain electrode layer, and the sidewalls; and
forming a gate electrode layer over the gate insulating layer so that the gate electrode layer overlaps with the sidewalls at least partly.
16. A semiconductor element comprising:
an oxide semiconductor layer over an insulating surface;
a source electrode layer and a drain electrode layer on the oxide semiconductor layer;
sidewalls provided in direct contact with a side surface of the source electrode layer and a side surface of the drain electrode layer;
a gate insulating layer over the oxide semiconductor layer, the sidewalls, the source electrode layer, and the drain electrode layer; and
a gate electrode layer on the gate insulating layer,
wherein the sidewalls are provided between the gate insulating layer and the source electrode layer and the drain electrode layer,
wherein the sidewalls and the gate electrode layer overlap at least partly with each other, and
wherein the sidewalls are in direct contact with a top surface of the oxide semiconductor layer.
4. A method for manufacturing a semiconductor element, comprising the steps of:
forming an oxide semiconductor layer over an insulating surface;
forming a source electrode layer and a drain electrode layer on the oxide semiconductor layer;
forming a film serving as sidewalls on the oxide semiconductor layer, the source electrode layer, and the drain electrode layer;
forming sidewalls by etching the film serving as the sidewalls, the sidewalls being in direct contact with a side surface of the source electrode layer, a side surface of the drain electrode layer, and a top surface of the oxide semiconductor layer;
forming a gate insulating layer over the oxide semiconductor layer, the source electrode layer, the drain electrode layer, and the sidewalls; and
forming a gate electrode layer over the gate insulating layer so that the gate electrode layer overlaps with the sidewalls at least partly.
28. A semiconductor element comprising:
an oxide semiconductor layer over and in contact with an insulating surface;
a pair of first conductive layers in contact with the oxide semiconductor layer, wherein the pair of first conductive layers is provided apart from each other in a channel length direction;
a pair of second conductive layers over the oxide semiconductor layer, wherein the pair of second conductive layers is provided apart from each other in a channel length direction;
a gate insulating layer over the oxide semiconductor layer, the pair of first conductive layers, and the pair of second conductive layers; and
a gate electrode layer over the gate insulating layer,
wherein one of the pair of second conductive layers is in contact with the oxide semiconductor layer and an inner side surface of one of the pair of first conductive layers,
wherein other of the pair of second conductive layers is in contact with the oxide semiconductor layer and an inner side surface of other of the pair of first conductive layers, and
wherein the pair of first conductive layers overlaps with the gate electrode layer.
7. A method for manufacturing a semiconductor element, comprising the steps of:
forming an oxide semiconductor layer over an insulating surface;
forming a first conductive film and a second conductive film on the oxide semiconductor layer;
forming a second source electrode layer and a second drain electrode layer by etching the second conductive film;
forming a film serving as sidewalls on the first conductive film, the second source electrode layer, and the second drain electrode layer;
forming sidewalls by etching the film serving as the sidewalls, the sidewalls being in direct contact with a side surface of the second source electrode layer and a side surface of the second drain electrode layer;
forming a first source electrode layer and a first drain electrode layer by etching the first conductive film using the sidewalls as masks so that the sidewalls are in direct contact with top surfaces of the first source electrode layer and the first drain electrode layer, the first source electrode layer extending beyond an edge of the second source electrode layer, and the first drain electrode layer extending beyond an edge of the second drain electrode layer;
forming a gate insulating layer over the oxide semiconductor layer, the first source electrode layer, the second source electrode layer, the first drain electrode layer, the second drain electrode layer, and the sidewalls; and
forming a gate electrode layer over the gate insulating layer so that the gate electrode layer overlaps with the sidewalls at least partly.
22. A semiconductor element comprising:
an oxide semiconductor layer over an insulating surface;
a source electrode layer and a drain electrode layer on the oxide semiconductor layer,
wherein the source electrode layer comprising:
a first source electrode layer; and
a second source electrode layer on the first source electrode layer,
wherein the drain electrode layer comprising:
a first drain electrode layer; and
a second drain electrode layer on the first drain electrode layer,
a first sidewall provided in direct contact with a side surface of the second source electrode layer and a top surface of the first source electrode layer,
a second sidewall provided in direct contact with a side surface of the second drain electrode layer and a top surface of the first drain electrode layer,
a gate insulating layer over the oxide semiconductor layer, the first sidewall, the second sidewall, the source electrode layer, and the drain electrode layer; and
a gate electrode layer on the gate insulating layer,
wherein the first sidewall and the second sidewall are provided between the gate insulating layer and the source electrode layer and the drain electrode layer,
wherein the first sidewall and the gate electrode layer overlap at least partly with each other,
wherein the second sidewall and the gate electrode layer overlap at least partly with each other,
wherein the first source electrode layer extends beyond an edge of the second source electrode layer, and
wherein the first drain electrode layer extends beyond an edge of the second drain electrode layer.
2. The method for manufacturing the semiconductor element according to
forming a conductive layer on the insulating surface; and
forming an insulating layer covering the conductive layer,
wherein the conductive layer overlaps with the semiconductor layer with the insulating layer interposed therebetween.
3. The semiconductor element according to
wherein the sidewalls comprise an insulating material.
5. The method for manufacturing the semiconductor element according to
forming a conductive layer on the insulating surface; and
forming an insulating layer covering the conductive layer,
wherein the conductive layer overlaps with the oxide semiconductor layer with the insulating layer interposed therebetween.
6. The semiconductor element according to
wherein the sidewalls comprise an insulating material.
8. The method for manufacturing the semiconductor element according to
wherein the gate insulating layer and an insulating layer are provided between the gate electrode layer and the second source electrode layer or the second drain electrode layer, and
wherein the second source electrode layer or the second drain electrode layer overlaps with a part of the gate electrode layer with the gate insulating layer and the insulating layer interposed therebetween.
9. The semiconductor element according to
wherein the sidewalls comprise an insulating material.
11. The semiconductor element according to
a conductive layer on the insulating surface; and
an insulating layer covering the conductive layer,
wherein the conductive layer overlaps with the semiconductor layer with the insulating layer interposed therebetween.
12. The semiconductor element according to
wherein the gate insulating layer and an insulating layer are provided between the gate electrode layer and the source electrode layer or the drain electrode layer, and
wherein the source electrode layer or the drain electrode layer overlaps with a part of the gate electrode layer with the gate insulating layer and the insulating layer interposed therebetween.
13. The semiconductor element according to
wherein the sidewalls comprise an insulating material.
14. A semiconductor device comprising the semiconductor element according to
wherein the semiconductor device is an electronic device selected from the group consisting of a laptop personal computer, a portable information terminal, an e-book reader, a mobile phone, and a digital camera.
15. The semiconductor element according to
wherein the semiconductor layer is an oxide semiconductor layer.
17. The semiconductor element according to
a conductive layer on the insulating surface; and
an insulating layer covering the conductive layer,
wherein the conductive layer overlaps with the oxide semiconductor layer with the insulating layer interposed therebetween.
18. The semiconductor element according to
wherein the sidewalls comprise an insulating material.
19. A semiconductor device comprising the semiconductor element according to
wherein the semiconductor device is an electronic device selected from the group consisting of a laptop personal computer, a portable information terminal, an e-book reader, a mobile phone, and a digital camera.
20. The semiconductor element according to
21. The semiconductor element according to
23. The semiconductor element according to
wherein the gate insulating layer and an insulating layer are provided between the gate electrode layer and the source electrode layer or the drain electrode layer, and
wherein the source electrode layer or the drain electrode layer overlaps with a part of the gate electrode layer with the gate insulating layer and the insulating layer interposed therebetween.
24. The semiconductor element according to
wherein the first sidewall and the second sidewall each comprise an insulating material.
25. A semiconductor device comprising the semiconductor element according to
wherein the semiconductor device is an electronic device selected from the group consisting of a laptop personal computer, a portable information terminal, an e-book reader, a mobile phone, and a digital camera.
26. The semiconductor element according to
27. The semiconductor element according to
29. The semiconductor element according to
a third conductive layer on the insulating surface; and
an insulating layer covering the third conductive layer,
wherein the third conductive layer overlaps with the oxide semiconductor layer with the insulating layer interposed therebetween.
30. The semiconductor element according to
31. The semiconductor element according to
32. The semiconductor element according to
33. A semiconductor device comprising the semiconductor element according to
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The present invention relates to a semiconductor element including an oxide semiconductor and a semiconductor device including the semiconductor element. The present invention relates to, for example, an electronic device including a semiconductor integrated circuit as a component. In addition, the present invention relates to a method for manufacturing the semiconductor element and the semiconductor device.
In this specification, a “semiconductor device” refers to all devices which can function by utilizing semiconductor characteristics, and electro-optical devices, semiconductor circuits, electronic components, and electronic devices are all included in the category of the semiconductor device.
In recent years, semiconductor devices have been developed to be used as an LSI, a CPU, or a memory. A CPU is an aggregation of semiconductor elements each provided with an electrode which is a connection terminal, which includes a semiconductor integrated circuit (including at least a transistor and a memory) separated from a semiconductor wafer.
A semiconductor circuit (IC chip) such as an LSI, a CPU, or a memory is mounted on a circuit board, for example, a printed wiring board, to be used as one of components of a variety of electronic devices.
Further, a semiconductor device capable of transmitting and receiving data has been developed. Such a semiconductor device is called a wireless tag, an RFID tag, or the like. Those put into practical use include a semiconductor circuit (IC chip) formed using an antenna and a semiconductor substrate in many cases.
A silicon-based semiconductor material has been known as a semiconductor material that can be used for a transistor; however, an oxide semiconductor has attracted attention as another material. As a material for the oxide semiconductor, zinc oxide and a material containing zinc oxide as a component are known. In addition, a transistor including an amorphous oxide (oxide semiconductor) having an electron carrier concentration of lower than 1018/cm3 is disclosed (Patent Documents 1 to 3).
Miniaturizing a semiconductor element by reduction in channel length L of the semiconductor element is given as a way to increase the operation speed of a circuit and reduce power consumption of the semiconductor integrated circuit manufactured using the semiconductor element including an oxide semiconductor.
The space between a source electrode layer and a drain electrode layer which are formed over an oxide semiconductor layer needs to be reduced in order to reduce a channel length L of a top-gate semiconductor element including an oxide semiconductor for miniaturization of the semiconductor element. However, reducing the space between the source electrode layer and the drain electrode layer through a photo process is limited. For that reason, it is difficult to manufacture a minute semiconductor element.
In view of the foregoing, an object of one embodiment of the present invention is to provide a top-gate semiconductor element including an oxide semiconductor, which has a short channel length L and can be miniaturized. In addition, an object of one embodiment of the present invention is to provide a method for manufacturing the semiconductor element.
Further, an object of one embodiment of the present invention is to increase the operation speed of a circuit, and furthermore, to reduce power consumption by using a minute semiconductor element which has a short channel length L in a semiconductor integrated circuit such as an LSI, a CPU, or a memory.
Further, an object of one embodiment of the present invention is to provide a highly reliable semiconductor element and a semiconductor device including the semiconductor element by improving the coverage of a source electrode layer and a drain electrode layer with a gate insulating layer to prevent a short circuit between the gate electrode layer and the source electrode layer or the drain electrode layer.
In a top-gate semiconductor element including an oxide semiconductor, sidewalls are provided for a source electrode layer and a drain electrode layer, whereby the semiconductor element can have a short channel length L and can be minute. In addition, the minute semiconductor element which has a short channel length L is used in a semiconductor integrated circuit such as an LSI, a CPU, or a memory, whereby the operation speed of the circuit can be increased, and furthermore, power consumption can be reduced.
Further, sidewalls are provided for a source electrode layer and a drain electrode layer in a top-gate semiconductor element including an oxide semiconductor, so that side surfaces of the source electrode layer and the drain electrode layer are tapered; thus, the coverage with a gate insulating layer can be improved and a short circuit between a gate electrode layer and the source electrode layer or the drain electrode layer can be prevented. Accordingly, a highly reliable semiconductor element can be manufactured.
A normally-off semiconductor element in which off-state current is small can be manufactured by using an oxide semiconductor layer which has a large energy gap and in which the hydrogen concentration is sufficiently reduced and the purity is increased by removal of impurities such as hydrogen and moisture. The use of the semiconductor element makes it possible to realize a semiconductor device whose power consumption due to leakage current is small.
One embodiment of the present invention is a semiconductor element. The semiconductor element includes an oxide semiconductor layer on an insulating surface; a source electrode layer and a drain electrode layer over the oxide semiconductor layer; a gate insulating layer over the oxide semiconductor layer, the source electrode layer, and the drain electrode layer; and a gate electrode layer over the gate insulating layer. The source electrode layer and the drain electrode layer have sidewalls which are in contact with a top surface of the oxide semiconductor layer.
One embodiment of the present invention is a semiconductor element. The semiconductor element includes an oxide semiconductor layer on an insulating surface, and a source electrode layer and a drain electrode layer over the oxide semiconductor layer. The source electrode layer includes a first source electrode layer and a second source electrode layer over the first source electrode layer. The drain electrode layer includes a first drain electrode layer and a second drain electrode layer over the first drain electrode layer. A sidewall provided for the second source electrode layer is in contact with a top surface of the first source electrode layer. A sidewall provided for the second drain electrode layer is in contact with a top surface of the first drain electrode layer. The semiconductor element also includes a gate insulating layer over the oxide semiconductor layer, the source electrode layer, the drain electrode layer, and the sidewalls, and a gate electrode layer over the gate insulating layer. The first source electrode layer extends beyond an edge of the second source electrode layer and the first drain electrode layer extends beyond an edge of the second drain electrode layer.
With any of the above structures, at least one of the above objects can be achieved.
A conductive layer may be formed below the oxide semiconductor layer. The semiconductor element of the present invention has another structure in which a conductive layer is provided on the insulating surface and a first insulating layer which covers the conductive layer is provided in each of the above structures, and the conductive layer overlaps with the oxide semiconductor layer with the first insulating layer interposed therebetween.
In order to reduce parasitic capacitance, the semiconductor element of the present invention has another structure in which the gate insulating layer and a second insulating layer are provided between the gate electrode layer and the source electrode layer or the drain electrode layer in each of the above structures. In other words, in the semiconductor element, the source electrode layer or the drain electrode layer overlaps with part of the gate electrode layer with the gate insulating layer and the second insulating layer interposed therebetween. By providing the gate insulating layer and the second insulating layer between the gate electrode layer and the source electrode layer or the drain electrode layer, the space between the gate electrode layer and the source electrode layer or the space between the gate electrode layer and the drain electrode layer is increased, whereby parasitic capacitance can be reduced.
When the second insulating layer is provided, in order that the source electrode layer and the drain electrode layer have tapered shapes, etching conditions such as a selectivity ratio of the second insulating layer to the source electrode layer or the drain electrode layer need to be controlled, which makes processing by etching difficult. Unless the source electrode layer and the drain electrode layer are tapered, a problem arises in that the coverage with the gate insulating layer stacked thereover is reduced. However, in the semiconductor element according to one embodiment of the present invention, sidewalls are provided on side surfaces of the source electrode layer and the drain electrode layer, which give tapered shapes to the source electrode layer and the drain electrode layer; thus, edges of the source electrode layer and the drain electrode layer do not need to be processed to have tapered shapes. Accordingly, the semiconductor element can be easily manufactured.
In each of the above structures, the carrier concentration in the oxide semiconductor layer is preferably lower than 1×1012/cm3. In addition, in each of the above structures, the off-state current of the semiconductor element is preferably less than 1×10−13 A.
One embodiment of the present invention is a semiconductor device including the semiconductor element having each of the above structures.
Further, a semiconductor circuit can be manufactured by combining a plurality of semiconductor elements each including an oxide semiconductor layer in which the hydrogen concentration is sufficiently reduced. As the semiconductor circuit, for example, an EDMOS circuit can be formed. The semiconductor device includes an EDMOS circuit which includes, on an insulating surface, a first semiconductor element including a first oxide semiconductor layer and a second semiconductor element including a second oxide semiconductor layer. The first oxide semiconductor layer and the second oxide semiconductor layer have a carrier concentration of lower than 1×1012/cm3.
Here, the EDMOS circuit refers to an inverter circuit including an enhancement mode transistor and a depletion mode transistor in combination.
As well as an LSI, a CPU, or a memory, a power supply circuit, a transmitting and receiving circuit, an amplifier of an audio processing circuit, a driver circuit of a display portion, a controller, a converter of an audio processing circuit, or the like can be manufactured using the semiconductor element having each of the above structures.
A plurality of semiconductor integrated circuits can be mounted on one package to increase the density of a semiconductor device, which is a so-called MCP (multi chip package).
Further, in the case where the semiconductor integrated circuit is mounted on a circuit board, the semiconductor integrated circuit may be mounted in a face-up state or a flip-chip state (face-down state).
One embodiment of the present invention is a method for manufacturing a semiconductor element. The method includes the steps of forming an oxide semiconductor layer on an insulating surface; forming a source electrode layer and a drain electrode layer over the oxide semiconductor layer; forming a film serving as a sidewall over the oxide semiconductor layer, the source electrode layer, and the drain electrode layer; forming sidewalls of the source electrode layer and the drain electrode layer, which are in contact with a top surface of the oxide semiconductor layer, by etching the film serving as a sidewall; forming a gate insulating layer over the oxide semiconductor layer, the source electrode layer, the drain electrode layer, and the sidewalls; and forming a gate electrode layer over the gate insulating layer.
One embodiment of the present invention is a method for manufacturing a semiconductor element. The method includes the steps of forming an oxide semiconductor layer on an insulating surface; forming a first conductive film and a second conductive film over the oxide semiconductor layer; forming a second source electrode layer and a second drain electrode layer by etching the second conductive film; forming a film serving as a sidewall over the first conductive film, the second source electrode layer, and the second drain electrode layer; forming sidewalls of the second source electrode layer and the second drain electrode layer by etching the film serving as a sidewall; forming a first source electrode layer and a first drain electrode layer by etching the first conductive film, using the sidewalls as masks; forming a gate insulating layer over the oxide semiconductor layer, the first source electrode layer, the second source electrode layer, the first drain electrode layer, the second drain electrode layer, and the sidewalls; and forming a gate electrode layer over the gate insulating layer. The first source electrode layer extends beyond an edge of the second source electrode layer. The first drain electrode layer extends beyond an edge of the second drain electrode layer. The sidewall is in contact with a top surface of the first source electrode layer or the first drain electrode layer.
One embodiment of the present invention is a method for manufacturing a semiconductor element in each of the above structures, which includes the steps of forming a conductive layer on the insulating surface; forming an insulating layer which covers the conductive layer; and forming the oxide semiconductor layer overlapping with the conductive layer with the insulating layer interposed therebetween.
Note that in this specification, the “channel length L” refers to the length in the direction connecting the source electrode layer and the drain electrode layer in a region where a bottom surface of a gate electrode layer overlap with an oxide semiconductor layer.
In this specification and the like, the terms “over” and “below” do not necessarily mean “directly on” and “directly below”, respectively, in the description of the positional relationship between components. For example, the expression of “a gate electrode layer over a gate insulating layer” does not exclude the case where another component is interposed between the gate insulating layer and the gate electrode layer. In addition, the terms “over” and “below” are used only for convenience of the description. Unless otherwise specified, the case where the positions thereof are interchanged is included.
In addition, in this specification and the like, the term such as “electrode” or “wiring” does not limit a function of a component. For example, an “electrode” is sometimes used as part of a “wiring”, and vice versa. Furthermore, the term “electrode” or “wiring” can include the case where a plurality of “electrodes” or “wirings” are formed in an integrated manner.
Functions of a “source” and a “drain” are sometimes replaced with each other when a transistor of opposite polarity is used or when the direction of current flowing is changed in circuit operation, for example. Therefore, the terms “source” and “drain” can be replaced with each other in this specification.
According to one embodiment of the present invention, a top-gate semiconductor element including an oxide semiconductor layer, which has a short channel length L and can be miniaturized can be provided by providing sidewalls for a source electrode layer and a drain electrode layer. In addition, according to one embodiment of the present invention, a method for manufacturing the semiconductor element can be provided.
Further, a minute semiconductor element which has a short channel length L according to one embodiment of the present invention is used in a semiconductor integrated circuit such as an LSI, a CPU, or a memory, whereby the operation speed of the circuit can be increased, and furthermore, power consumption can be reduced.
Further, in the semiconductor element according to one embodiment of the present invention, the sidewalls are provided on the side surfaces of the source electrode layer and the drain electrode layer, which give tapered shapes to the source electrode layer and the drain electrode layer; thus, the coverage with a gate insulating layer can be improved and a short circuit between a gate electrode layer and the source electrode layer or the drain electrode layer can be prevented. Accordingly, a highly reliable semiconductor element can be manufactured.
Hereinafter, Embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the description below, and it is easily understood by those skilled in the art that the modes and details disclosed herein can be modified in various ways without departing from the spirit and scope of the present invention. Further, the present invention is not construed as being limited to the description of Embodiments.
Note that the position, size, range, or the like of each component illustrated in the drawings and the like is not accurately represented in some cases for easy understanding. Therefore, the disclosed invention is not necessarily limited to the position, size, range, or the like as disclosed in the drawings and the like.
In this specification and the like, ordinal numbers such as “first”, “second”, and “third” are used in order to avoid confusion among components, and the terms do not mean limitation of the number of components.
In this embodiment, an example of a cross-sectional structure of a semiconductor element according to one embodiment of the present invention will be described.
A semiconductor element of this embodiment will be described with reference to
The transistor 200 illustrated in
The transistor 200 includes the sidewalls 121 of the source electrode layer 109a and the drain electrode layer 109b. Bottom surfaces of the sidewalls 121 are in contact with a top surface of the oxide semiconductor layer 107. Reduction in the space between the source electrode layer 109a and the drain electrode layer 109b through a photo process is limited. However, when the sidewalls 121 are provided in the space by anisotropic etching, the width of part of the gate electrode layer 119, which is positioned between the source electrode layer 109a and the drain electrode layer 109b can be reduced; thus, a minute transistor which has a short channel length L can be manufactured. Reduction in the channel length L might cause a short-channel effect. The short-channel effect in a transistor including an oxide semiconductor will be described later in this embodiment.
Note that the “channel length L” in this specification refers to the length in the direction connecting the source electrode layer and the drain electrode layer in a region where a bottom surface of the gate electrode layer overlap with the oxide semiconductor layer (
In the transistor 200, sidewalls are provided on side surfaces of the source electrode layer and the drain electrode layer, which give tapered shapes to the source electrode layer and the drain electrode layer; thus, the coverage with the gate insulating layer can be improved and a short circuit between the gate electrode layer and the source electrode layer or the drain electrode layer can be prevented. Thus, the transistor 200 can be highly reliable.
When the sidewall 121 is formed using an insulating material, an offset region Loff is provided as illustrated in
In contrast, in the case where the sidewall 121 is formed using a conductive material, the sidewall 121 functions as a part of the source electrode layer or the drain electrode layer; thus, the offset region Loff can be reduced (
In other words, the offset region Loff can be both increased and decreased by changing a material used for the sidewall 121.
Further, the transistor 200 includes the purified oxide semiconductor layer 107 as a channel region. The transistor 200 including the purified oxide semiconductor which has a large energy gap has small off-state current and an electric characteristic of being normally off (that is, current does not flow between the source electrode and the drain electrode when the gate voltage is 0 V), and further, has small temperature dependence of the transistor characteristics. For example, in the case where the drain voltage Vd is +1 V or +10 V the drain current Id is sufficiently high when the gate voltage Vg is positive, and the drain current can be lower than or equal to 1×10−13 A when the gate voltage Vg ranges from −5 V to −20 V.
Note that the carrier concentration in the oxide semiconductor layer 107 in which the hydrogen concentration is sufficiently reduced and the purity is increased is lower than 1×1012/cm3, preferably lower than or equal to 1×1011/cm3, more preferably lower than or equal to 1.45×1010/cm3. A method for calculating the carrier concentration will be described later in this embodiment.
The energy gap of the oxide semiconductor layer 107 is greater than or equal to 2.0 eV, preferably greater than or equal to 2.5 eV, more preferably greater than or equal to 3.0 eV. Comparison with another material having a large energy gap will be described later. In addition, a transistor including an oxide semiconductor which is purified and has low carrier concentration has high resistance to hot carrier degradation. This will be also specifically described later.
As described above, the normally-off transistor 200 is manufactured by using the oxide semiconductor layer 107 which has a large energy gap and in which the hydrogen concentration is sufficiently reduced and the purity is increased, so that a semiconductor device having a novel structure can be realized.
The transistor 201 illustrated in
In other words, the transistor 201 has a structure in which the electrode layer 102 is added to the transistor 200.
The electrode layer 102 provided below the oxide semiconductor layer 107 of the transistor 201 can function as a back gate. The potential of the back gate can be fixed potential, for example, 0 V, or ground potential, and may be determined by a practitioner as appropriate. By providing the gate electrodes above and below the oxide semiconductor layer, in a bias-temperature stress test (hereinafter, referred to as a BT test) for examining the reliability of the transistor, the amount of change in threshold voltage of the transistor before and after the BT test can be reduced. In other words, the provision of the gate electrodes above and below the oxide semiconductor layer allows the reliability to be improved.
Further, the threshold voltage can be controlled by controlling gate voltage applied to the electrode layer 102. The transistor can function as an enhancement mode transistor by setting the threshold voltage to be positive. Alternatively, the transistor can function as a depletion mode transistor by setting the threshold voltage to be negative.
For example, an inverter circuit including an enhancement mode transistor and a depletion mode transistor in combination (an EDMOS inverter circuit; hereinafter simply referred to as an EDMOS circuit) can be used for a driver circuit. The driver circuit includes at least a logic circuit portion, and a switch portion or a buffer portion. The logic circuit portion has a circuit structure including the above EDMOS circuit. Further, a transistor in which large on-state current can flow is preferably used for the switch portion or the buffer portion. A depletion mode transistor or a transistor including gate electrodes above and below an oxide semiconductor layer is used.
Further, transistors having different structures can be manufactured over one substrate without significant increase in the number of manufacturing steps. For example, an EDMOS circuit can be formed using the transistor including gate electrodes above and below an oxide semiconductor layer as illustrated in
Note that an n-channel transistor whose threshold voltage is positive is defined as an enhancement mode transistor while an n-channel transistor whose threshold voltage is negative is defined as a depletion mode transistor, throughout this specification.
The transistor 300 illustrated in
The transistor 300 includes the sidewalls 321 of the second source electrode layer 311a and the second drain electrode layer 311b. Bottom surfaces of the sidewalls 321 are in contact with top surfaces of the first source electrode layer 309a and the first drain electrode layer 309b. The transistor 300 includes the sidewalls 321, so that the transistor has a short channel length L. Reduction in the channel length L might cause a short-channel effect. A short-channel effect in a transistor including an oxide semiconductor will be described later in this embodiment.
The transistor 300 includes the third insulating layer 315. The provision of the third insulating layer 315 allows reduction in parasitic capacitance between the gate electrode layer 319 and the second source electrode layer 311a or between the gate electrode layer 319 and the second drain electrode layer 311b. Meanwhile, when the third insulating layer 315 is provided, in order that the second source electrode layer 311a and the second drain electrode layer 311b have tapered shapes, etching conditions such as a selectivity ratio of the third insulating layer 315 to the second source electrode layer 311a or the second drain electrode layer 311b need to be controlled, which makes processing by etching difficult. Unless the second source electrode layer 311a and the second drain electrode layer 311b are tapered, a problem arises in that the coverage with the gate insulating layer 317 stacked thereover is reduced. However, in the transistor according to one embodiment of the present invention, the sidewalls 321 are provided on side surfaces of the second source electrode layer 311a and the second drain electrode layer 311b, which give tapered shapes to the source electrode layer 311a and the drain electrode layer 311b; thus, the edges of the second source electrode layer 311a and the second drain electrode layer 311b do not need to be processed to have tapered shapes. Accordingly, the transistor can be easily manufactured.
The transistor 300 is different from the transistors 200 and 201 in that an offset region Loff does not depend on a material for the sidewalls but is determined by the thickness of the gate insulating layer.
As described above, an oxide semiconductor which is made to be intrinsic or substantially intrinsic by removing impurities which can be carrier donors (donors or acceptors) in the oxide semiconductor to a very low level is used in the transistor of this embodiment.
The significance of purifying an oxide semiconductor and making an oxide semiconductor intrinsic (i-type), advantages of manufacturing a semiconductor device using the oxide semiconductor, and the like will be briefly described below.
<Making Oxide Semiconductor Intrinsic>
Note that, although a lot of researches on properties, such as density of state (DOS), of an oxide semiconductor have been conducted, they do not include the idea of sufficiently reducing localized states themselves. According to one embodiment of the disclosed invention, a purified oxide semiconductor is formed by removing water or hydrogen, which might be a cause of localized states, from the oxide semiconductor. This is based on the idea of sufficiently reducing localized states themselves, and makes it possible to manufacture excellent industrial products.
Note that when hydrogen, water, or the like is removed, oxygen is also removed in some cases. Therefore, it is preferable that the oxide semiconductor be further purified (made to be i-type) by supplying oxygen to dangling bonds of metal which are formed due to oxygen vacancy so that localized states resulted from oxygen defects are reduced. For example, the localized states resulted from the oxygen defects can be reduced in the following manner: an oxide film having excess oxygen is formed in a close contact with a channel formation region; and heat treatment at 200° C. to 400° C., typically, approximately 250° C., is performed so that oxygen is supplied to the oxide semiconductor from the oxide film. An inert gas may be switched to a gas containing oxygen during second heat treatment described later. Further, after the second heat treatment, oxygen can be supplied to the oxide semiconductor through a temperature decreasing process in an oxygen atmosphere or an atmosphere from which hydrogen, water, or the like has been sufficiently reduced.
A factor that deteriorates characteristics of an oxide semiconductor is thought to be a shallow level due to excess hydrogen at 0.1 eV to 0.2 eV below the conduction band, a deep level due to oxygen vacancy, or the like. Therefore, the technical idea that hydrogen is reduced as much as possible and oxygen is adequately supplied in order to eliminate such a defect would be right.
An oxide semiconductor is generally considered as an n-type semiconductor; however, according to one embodiment of the disclosed invention, an i-type oxide semiconductor is realized by removing impurities such as water or hydrogen and supplying oxygen which is a constituent element of the oxide semiconductor. In this respect, it can be said that one embodiment of the invention disclosed herein includes a novel technical idea because the oxide semiconductor according to one embodiment of the invention is made to be i-type in a manner different from that of silicon or the like which is made to be i-type by addition of impurities.
Further, an oxide semiconductor is made to be i-type, so that a transistor has favorable temperature characteristics; typically, as for the current-voltage characteristics of the transistor, in the temperature range of −25° C. to 150° C., there are few variations in on-state current, off-state current, field effect mobility, S value, and threshold voltage and there is little deterioration of the current-voltage characteristics due to temperature.
The technical idea of this embodiment is that impurities are not further added to an oxide semiconductor and, on the contrary, the oxide semiconductor itself is purified by removing impurities such as water and hydrogen which undesirably exist therein. In other words, an oxide semiconductor is purified by intentionally removing water or hydrogen which forms a donor level to further reduce oxygen vacancy and adequately supplying oxygen which is a main component of the oxide semiconductor.
The concentration of hydrogen in an as-deposited oxide semiconductor is measured by secondary ion mass spectrometry (SIMS) to be on the order of 1020/cm3. The oxide semiconductor is made to have higher purity to be electrically i-type (intrinsic) semiconductor by intentionally removing water or hydrogen which causes a donor level and further adding oxygen (one of components of the oxide semiconductor) which is reduced at the same time as the removal of water or hydrogen.
In this embodiment, the amount of water and hydrogen in an oxide semiconductor is preferably smaller and the amount of carriers is also preferably smaller. In other words, the carrier concentration is preferably lower than 1×1012/cm3, more preferably lower than 1.45×1010/cm3. Furthermore, the ideal carrier concentration is close to zero or zero according to the technical idea of this embodiment. In particular, the oxide semiconductor can be purified by removing water or hydrogen which serves as an n-type impurity by heat treatment at a temperature higher than or equal to 450° C. and lower than or equal to 850° C., preferably higher than or equal to 550° C. and lower than or equal to 750° C. in an oxygen atmosphere, a nitrogen atmosphere, or an ultra-dry (air containing water at 20 ppm or less, preferably 1 ppm or less, more preferably 10 ppb or less) atmosphere. The oxide semiconductor is purified by removing impurities such as water or hydrogen, whereby the carrier concentration can be lower than 1×1012/cm3, preferably lower than 1.45×1010/cm3. The carriers in the oxide semiconductor are reduced or preferably eliminated, so that the oxide semiconductor functions as a path in a transistor through which carriers pass.
As described above, the oxide semiconductor is purified so that impurities that are not main components of the oxide semiconductor film, typically hydrogen, water, hydroxyl, or hydride, are contained as little as possible, whereby favorable operation of the transistor can be obtained. In addition, the amount of change in threshold voltage of the transistor before and after the BT test can be suppressed, whereby high reliability can be realized. Moreover, the temperature dependence of the electric characteristics can be suppressed.
<Comparison with Another Semiconductor Material>
Silicon carbide (e.g., 4H—SiC) is given as an example of a semiconductor material which can be compared with an oxide semiconductor. An oxide semiconductor and 4H—SiC have some things in common. The carrier concentration is one example thereof. In accordance with Fermi-Dirac distribution at normal temperature, the concentration of minority carriers in an oxide semiconductor is estimated to be approximately 10−7/cm3, which is extremely low like the carrier concentration in 4H—SiC, that is, 6.7×10−11/cm3. When the minority carrier concentration in the oxide semiconductor is compared with the intrinsic carrier concentration in silicon (approximately 1.45×1010/cm3), it can be well understood that the minority carrier concentration in the oxide semiconductor is significantly low.
In addition, the energy band gap of the oxide semiconductor is 3.0 eV to 3.5 eV and that of 4H—SiC is 3.26 eV, which means that both the oxide semiconductor and silicon carbide are common in that both are wide-gap semiconductors.
On the other hand, there is a major difference between the oxide semiconductor and silicon carbide. That is the process temperature. Since silicon carbide generally needs to be subjected to heat treatment at 1500° C. to 2000° C., it is difficult to form a stack of silicon carbide and a semiconductor element formed using a semiconductor material which is not silicon carbide. This is because a semiconductor substrate, a semiconductor element, and the like are damaged by such high temperature. In contrast, the oxide semiconductor can be formed by heat treatment at 300° C. to 800° C.; therefore, it is possible to form an integrated circuit with the use of a semiconductor material which is not an oxide semiconductor and then to form a semiconductor element with the use of an oxide semiconductor.
In contrast to the case of using silicon carbide, in the case of using an oxide semiconductor, there is an advantage that a low heat-resistant substrate such as a glass substrate can be used. In addition, in the case of using an oxide semiconductor, heat treatment at high temperature is not needed, so that the energy cost can be sufficiently reduced as compared to the case of using silicon carbide. In silicon carbide, a crystal defect or a small amount of impurities involuntarily mixed causes carriers. Therefore, it is actually difficult to obtain a carrier concentration of lower than or equal to 1012/cm3 for the reason given above though, in theory, it is possible to obtain a low carrier concentration in silicon carbide which is equal to that of the oxide semiconductor of one embodiment of the present invention. The same can be said for the comparison between the oxide semiconductor and gallium nitride that is also known as a wide-gap semiconductor.
<Electrical Conduction Mechanism of Transistor Including Oxide Semiconductor>
Here, the electrical conduction mechanism of a transistor including an oxide semiconductor is described with reference to
At normal temperature, electrons in the metal are degenerated and the Fermi level is located in the conduction band. In contrast, a conventional oxide semiconductor is generally an n-type semiconductor, and the Fermi level (EF) is away from the intrinsic Fermi level (Ei) located in the middle of the band gap and is located closer to the conduction band. Note that it is known that some hydrogen in the oxide semiconductor serves as a donor and is one of the factors that cause the oxide semiconductor to be an n-type semiconductor.
In contrast, the oxide semiconductor according to one embodiment of the disclosed invention is an oxide semiconductor that is made to be intrinsic (i-type) or substantially intrinsic by being purified by removal of hydrogen in the oxide semiconductor, which causes an n-type oxide semiconductor, so that impurities that are not main components of the oxide semiconductor are prevented from being contained therein as much as possible. In other words, the oxide semiconductor according to one embodiment of the present invention has a feature in that it is made to be an i-type (intrinsic) semiconductor or made to be close thereto not by addition of impurities but by being purified by removal of impurities such as hydrogen or water as much as possible. This enables the Fermi level (EF) to be at substantially the same level as the intrinsic Fermi level (Ei).
It is said that the electron affinity (χ) of an oxide semiconductor is 4.3 eV in the case where the band gap (Eg) thereof is 3.15 eV. The work function of titanium (Ti) used for forming the source electrode layer and the drain electrode layer is substantially equal to the electron affinity (χ) of the oxide semiconductor. In that case, the Schottky electron barrier is not formed at an interface between the metal and the oxide semiconductor.
At this time, as shown in
As shown in
As described above, the oxide semiconductor is made to be intrinsic (i-type) or substantially intrinsic by being purified so that elements that are not main components thereof (i.e., impurity elements) are contained as little as possible. Thus, the characteristics of the interface between the oxide semiconductor and the gate insulating layer become obvious. For that reason, the gate insulating layer needs to form a favorable interface with the oxide semiconductor. Specifically, it is preferable to use the following insulating layer, for example: an insulating layer formed by a CVD method using high-density plasma generated with a power supply frequency in the range of the VHF band to the microwave band or an insulating layer formed by a sputtering method.
The interface between the oxide semiconductor and the gate insulating layer is made favorable while the oxide semiconductor is purified, whereby an off-state current of less than or equal to 1×10−13 A and a subthreshold swing (S value) of 0.1 V/dec. (the thickness of the gate insulating layer: 100 nm) can be realized at normal temperature in the case where a transistor has, for example, a channel width W of 1×104 μm and a channel length L of 3 μm.
The oxide semiconductor is purified as described above so as to contain elements that are not main components of the oxide semiconductor (i.e., impurity elements) as little as possible, whereby favorable operation of the transistor can be obtained.
<Resistance of Transistor Including Oxide Semiconductor to Hot Carrier Degradation>
Next, the resistance of a transistor including an oxide semiconductor to hot carrier degradation will be described with reference to
Main causes of hot carrier degradation are channel hot electron injection (CHE injection) and drain avalanche hot carrier injection (DAHC injection). Note that only electrons are considered below for simplicity.
CHE injection refers to a phenomenon in which electrons having gained energy higher than the barrier of a gate insulating layer in a semiconductor layer are injected into the gate insulating layer or the like. Electrons gain energy by being accelerated by a low electric field.
DAHC injection refers to a phenomenon in which electrons generated by collision of electrons accelerated by a high electric field are injected into a gate insulating layer or the like. A difference between DAHC injection and CHE injection is whether or not they involve avalanche breakdown caused by impact ionization. Note that DAHC injection requires electrons having a kinetic energy higher than the band gap of a semiconductor.
Regarding silicon, degradation caused by DAHC injection is more serious than that caused by CHE injection. This results from the fact that carriers (e.g., electrons) which are accelerated without colliding are very few in silicon whereas silicon has a narrow band gap and avalanche breakdown readily occurs therein. The avalanche breakdown increases the number of electrons capable of travelling over the barrier of the gate insulating layer, and the probability of hot electrons in that case is higher than that of hot electrons in the case where the avalanche breakdown does not occur.
Regarding an In—Ga—Zn—O-based oxide semiconductor, the energy required for CHE injection does not greatly differ from that in the case of silicon, and the probability of CHE injection is still low similarly to silicon. However, because of the wide band gap, the energy required for DAHC injection is substantially equal to the energy required for CHE injection and higher than that in the case of silicon; thus, DAHC injection is less likely to occur in the first place.
In other words, the probabilities of both CHE injection and DAHC injection are low and the resistance to hot carrier degradation is higher than that of silicon.
The band gap of an In—Ga—Zn—O-based oxide semiconductor is comparable to that of silicon carbide (SiC) which attracts attention as a material having high withstand voltage.
As described above, it can be seen that an In—Ga—Zn—O-based oxide semiconductor has significantly higher resistance to hot carrier degradation and higher resistance to source-drain breakdown than silicon. It can also be said that withstand voltage comparable to that of silicon carbide can be obtained.
<Short-Channel Effect in Transistor Including Oxide Semiconductor>
Next, a short-channel effect in a transistor including an oxide semiconductor will be described with reference to
The short-channel effect refers to degradation of electrical characteristics which become obvious with miniaturization of a transistor (a reduction in channel length (L)). The short-channel effect results from the influence of electric field distribution in the vicinity of a drain on a source. Specific examples of the short-channel effect are a decrease in threshold voltage, an increase in subthreshold swing (S value), an increase in leakage current, and the like.
Here, a structure with which a short-channel effect can be suppressed was examined using calculation results (by device simulation). Specifically, four kinds of models each having a different carrier concentration and a different thickness of an oxide semiconductor layer were prepared, and the relation between a channel length (L) and threshold voltage (Vth) was examined. As the models, bottom-gate transistors were employed, each of which had a carrier concentration of 1.7×10−8/cm3 or 1.0×1015/cm3 and an oxide semiconductor layer with a thickness of 1 μm or 30 nm. Note that an In—Ga—Zn—O-based oxide semiconductor was used as the oxide semiconductor, and a silicon oxynitride film with a thickness of 100 nm was used as a gate insulating layer. The band gap, electron affinity, relative permittivity, and electron mobility of the oxide semiconductor were assumed to be 3.15 eV, 4.3 eV, 15, and 10 cm2/Vs, respectively. The relative permittivity of the silicon oxynitride film was assumed to be 4.0. The calculation was performed using device simulation software “ATLAS” produced by SILVACO, Inc.
Note that there is no significant difference in calculation results between a top-gate transistor and a bottom-gate transistor.
<Carrier Concentration>
The technical idea according to the disclosed invention is making an oxide semiconductor layer as close as possible to an intrinsic (i-type) semiconductor layer by sufficiently reducing the carrier concentration therein. A method for calculating the carrier concentration and the actually measured carrier concentration will be described below with reference to
First, a method for calculating the carrier concentration is briefly explained. The carrier concentration can be calculated in such a manner that a MOS capacitor is manufactured and the results of C-V measurement (capacitance voltage measurement) (i.e., C-V characteristics) of the MOS capacitor are evaluated.
Specifically, carrier concentration N, is calculated in the following manner: C-V characteristics are obtained by plotting relations between a gate voltage (Vg) and a capacitance (C) of an MOS capacitor; a graph of a relation between the gate voltage Vg and (1/C)2 is obtained with the use of the C-V characteristics; a differential value of (1/C2 in a weak inversion region of the graph is calculated; and the differential value is substituted into Formula 1. Note that q, ∈0, and ∈ in Formula 1 represent elementary electric charge, vacuum permittivity, and relative permittivity of an oxide semiconductor, respectively.
Next, the carrier concentration actually measured by the above method will be described. For the measurement, a sample (an MOS capacitor) which was formed as follows was used: a titanium film was formed to a thickness of 300 nm over a glass substrate; a titanium nitride film was formed to a thickness of 100 nm over the titanium film; an oxide semiconductor layer using an In—Ga—Zn—O-based oxide semiconductor was formed to a thickness of 2 μm over the titanium nitride film; and a silver film was formed to a thickness of 300 nm over the oxide semiconductor layer. Note that the oxide semiconductor layer was formed using an oxide semiconductor target for film formation containing In, Ga, and Zn (e.g., a target having a composition ratio of In2O3:Ga2O3:ZnO=1:1:1 (molar ratio), a composition ratio of In2O3:Ga2O3:ZnO=1:1:2 (molar ratio), or In2O3:Ga2O3:ZnO=1:1:4 (molar ratio)) or the like by a sputtering method. Further, the oxide semiconductor layer was formed in a mixed atmosphere of argon and oxygen (the flow rates of Ar and O2 were 30 seem and 15 seem, respectively).
In this manner, by using an i-type or substantially i-type oxide semiconductor having a large energy gap (e.g., with a carrier concentration of lower than 1×1012/cm3, preferably lower than 1.45×1010/cm3), a normally-off transistor with excellent off-state current characteristics can be obtained.
Accordingly, the semiconductor element of one embodiment of the present invention is a semiconductor which is made to be intrinsic or substantially intrinsic by removal of impurities which serve as electron donors (donors) in an oxide semiconductor, and a channel region is preferably formed using an oxide semiconductor which has a larger energy gap than a silicon semiconductor. A semiconductor element including an oxide semiconductor which has a large energy gap and in which the hydrogen concentration is sufficiently reduced mid the purity is increased is manufactured, whereby a normally-off semiconductor device in which off-state current is small and the temperature dependence of transistor characteristics is small can be realized. In addition, the use of the semiconductor element makes it possible to realize a semiconductor device whose power consumption due to leakage current is small.
According to the semiconductor element of one embodiment of the present invention, a top-gate semiconductor element including an oxide semiconductor, which to has a short channel length L and can be miniaturized can be realized by providing sidewalls for a source electrode layer and a drain electrode layer.
Further, the semiconductor element of one embodiment of the present invention has a short channel length L and can be miniaturized; thus, when the semiconductor element is used in a semiconductor integrated circuit such as an LSI, a CPU, or a memory, the operation speed of the circuit is increased, and furthermore, power consumption can be reduced.
Further, in the semiconductor element of one embodiment of the present invention, sidewalls are provided on side surfaces of a source electrode layer and a drain electrode layer, which give tapered shapes to the source electrode layer and the drain electrode layer; thus, the coverage with a gate insulating layer can be increased and a short circuit between a gate electrode layer and the source electrode layer or the drain electrode layer can be prevented. As a result, a highly reliable semiconductor element and a highly reliable semiconductor device including the semiconductor element can be realized.
This embodiment can be freely combined with any of the other embodiments.
In this embodiment, an example of a method for manufacturing a semiconductor element will be described. One embodiment of a method for manufacturing a semiconductor element of this embodiment will be described with reference to
A process of manufacturing the transistors 200 and 201, which are described in Embodiment 1, over the substrate 101 having an insulating surface will be described below.
Although there is no particular limitation on a substrate which can be used as the substrate 101 having an insulating surface, the substrate needs to have heat resistance high enough to withstand at least heat treatment performed later. For example, a glass substrate made of aluminosilicate glass, barium borosilicate glass, aluminoborosilicate glass, or the like can be used.
Note that a substrate formed of an insulator such as a ceramic substrate, a quartz substrate, or a sapphire substrate may be used instead of the glass substrate. Alternatively, a crystallized glass substrate or the like may be used. Alternatively, a semiconductor substrate including an insulating layer on its surface, a plastic substrate, or the like can be used as appropriate.
First, the first insulating layer 103 is formed over the substrate 101 having an insulating surface. The first insulating layer 103 can be formed to have a single-layer or stacked-layer structure using a silicon oxide layer, a silicon nitride layer, a silicon oxynitride layer, or a silicon nitride oxide layer by a plasma CVD method, a sputtering method, or the like.
In the case where the transistor 201 described in Embodiment 1 is manufactured, after a conductive film is formed over the substrate 101 having an insulating surface, the electrode layer 102 is formed in a photolithography step, and then the first insulating layer 103 for covering the electrode layer 102 is formed. The electrode layer 102 can be formed using an element selected from Al, Cr, Cu, Ta, Ti, Mo, and W, an alloy containing any of these elements, an alloy containing any of these elements in combination, or the like. In this embodiment, the electrode layer 102 has a structure in which a tungsten nitride layer and a tungsten layer are stacked.
Next, the second insulating layer 105 is formed over the first insulating layer 103. As the second insulating layer 105 which is in contact with an oxide semiconductor layer, an oxide insulating layer such as a silicon oxide layer, a silicon oxynitride layer, an aluminum oxide layer, or an aluminum oxynitride layer is preferably used. As a method for forming the second insulating layer 105, a plasma CVD method, a sputtering method, or the like can be used; however, it is preferable that the second insulating layer 105 be formed by a sputtering method in order to prevent a large amount of hydrogen from being contained in the second insulating layer 105.
In this embodiment, as the second insulating layer 105, a silicon oxide layer is formed by a sputtering method. The substrate 101 is transferred to a treatment chamber, a sputtering gas which contains high-purity oxygen and from which hydrogen and moisture have been removed is introduced thereinto, and a silicon oxide layer is formed as the second insulating layer 105 over the substrate 101 with the use of a silicon target. The substrate 101 may be at room temperature or may be heated.
For example, the silicon oxide layer is formed by an RF sputtering method under the following conditions: quartz (preferably synthetic quartz) is used, the substrate temperature is 108° C., the distance between the substrate and the target (the T−S distance) is 60 mm, the pressure is 0.4 Pa, the high-frequency electric power is 1.5 kW, the atmosphere is an atmosphere containing oxygen and argon (the flow ratio of oxygen to argon is 1:1 (each flow rate is 25 sccm)). The thickness of the silicon oxide layer is 100 nm. Instead of quartz (preferably synthetic quartz), a silicon target can be used as a target for forming the silicon oxide layer. As a sputtering gas, oxygen or a mixed gas of oxygen and argon is used.
In this case, it is preferable that the second insulating layer 105 be formed while moisture remaining in the treatment chamber is removed so that hydrogen, hydroxyl, or moisture is prevented from being contained in the second insulating layer 105.
In order to remove moisture remaining in the treatment chamber, an entrapment vacuum pump is preferably used. For example, a cryopump, an ion pump, or a titanium sublimation pump is preferably used. Further, an evacuation unit may be a turbo pump provided with a cold trap. From the treatment chamber evacuated with a cryopump, for example, a hydrogen atom, a compound containing a hydrogen atom such as water (H2O), and the like are removed; thus, the concentration of impurities in the second insulating layer 105 formed in the treatment chamber can be reduced.
The second insulating layer 105 may have a stacked-layer structure. For example, the second insulating layer 105 may have a structure in which a nitride insulating layer such as a silicon nitride layer, a silicon nitride oxide layer, or an aluminum nitride layer and the above oxide insulating layer are stacked in this order over the substrate 101.
For example, a silicon nitride layer is formed between the silicon oxide layer and the substrate by introducing a sputtering gas which contains high-purity nitrogen and from which hydrogen and moisture have been removed and using a silicon target. In this case also, it is preferable that the silicon nitride layer be formed while moisture remaining in the treatment chamber is removed in a manner similar to that of the silicon oxide layer.
The substrate may be heated also at the time of the formation of the silicon nitride layer.
In the case where the silicon nitride layer and the silicon oxide layer are stacked to form the second insulating layer 105, the silicon nitride layer and the silicon oxide layer can be formed in the same treatment chamber using the same silicon target. First, a sputtering gas containing nitrogen is introduced and a silicon nitride layer is formed using a silicon target placed inside the treatment chamber, and then the sputtering gas is switched to a sputtering gas containing oxygen and a silicon oxide layer is formed using the same silicon target. Since the silicon nitride layer and the silicon oxide layer can be formed in succession without being exposed to air, impurities such as hydrogen or moisture can be prevented from being adsorbed on a surface of the silicon nitride layer.
Next, an oxide semiconductor film is formed to a thickness of greater than or equal to 3 nm and less than or equal to 50 nm over the second insulating layer 105. It is particularly preferable to form an oxide semiconductor film with a thickness of greater than or equal to 3 nm and less than or equal to 20 nm in order to sufficiently suppress a short-channel effect.
The oxide semiconductor film is formed using an oxide semiconductor which has a large energy gap and is purified by sufficiently removing impurities such as hydrogen which serve as electron donors (donors) in the oxide semiconductor.
The carrier concentration can be measured by Hall effect measurement. The carrier concentration in the oxide semiconductor which is measured by Hall effect measurement is equivalent to 1.45×1010/cm3, which is the intrinsic carrier concentration in silicon, or lower. In accordance with Fermi-Dirac distribution at normal temperature, the intrinsic carrier concentration in an oxide semiconductor which has an energy gap of 3 eV or more is 10−7/cm3 while the intrinsic carrier concentration in silicon is 1010/cm3. In other words, the intrinsic carrier concentration in the oxide semiconductor is extremely close to zero.
The carrier concentration in the oxide semiconductor layer 107 used in this embodiment is lower than 1×1012/cm3, preferably lower than 1×1011/cm3, and the carrier concentration therein can be made to be extremely close to zero.
In order that hydrogen, hydroxyl, and moisture are contained as little as possible in the oxide semiconductor film, as pretreatment for the formation of the oxide semiconductor film, the substrate 101 over which the second insulating layer 105 is formed is preferably preheated in a preheating chamber of a sputtering apparatus, whereby impurities such as hydrogen or moisture adsorbed on the substrate 101 are eliminated and removed. As an evacuation unit provided for the preheating chamber, a cryopump is preferably used. Note that this preheating treatment can be omitted.
Note that before the oxide semiconductor film is formed by a sputtering method, dust attached to a surface of the second insulating layer 105 is preferably removed by reverse sputtering in which plasma is generated by introduction of an argon gas. The reverse sputtering refers to a method in which, without application of voltage to a target side, a high-frequency power source is used for application of voltage to a substrate side in an argon atmosphere to generate plasma in the vicinity of the substrate to modify a surface. Note that instead of an argon atmosphere, a nitrogen atmosphere, a helium atmosphere, an oxygen atmosphere, or the like may be used.
The oxide semiconductor film is formed by a sputtering method. As the oxide semiconductor film, the following can be used: a four-component metal oxide film such as an In—Sn—Ga—Zn—O-based film; a three-component metal oxide film such as an In—Ga—Zn—O-based film, an In—Sn—Zn—O-based film, an In—Al—Zn—O-based film, a Sn—Ga—Zn—O-based film, an Al—Ga—Zn—O-based film, or a Sn—Al—Zn—O-based film; or a two-component metal oxide film such as an In—Zn—O-based film, a Sn—Zn—O-based film, an Al—Zn—O-based film, a Zn—Mg—O-based film, a Sn—Mg—O-based film, or an In—Mg—O-based film; or a single-component metal oxide film such as an In—O-based film, a Sn—O-based film, or a Zn—O-based film. In addition, the above oxide semiconductor film may contain SiO2.
As the oxide semiconductor film, a thin film represented by InMO3 (ZnO), (m>0) can be used. Here, M represents one or more metal elements selected from Ga, Al, Mn, and Co. For example, M may be Ga, Ga and Al, Ga and Mn, Ga and Co, or the like.
In this embodiment, the oxide semiconductor film is formed by a sputtering method with the use of an In—Ga—Zn—O-based oxide semiconductor target for film formation. The oxide semiconductor film can be formed by a sputtering method in a rare gas (typically, argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas (typically, argon) and oxygen. In the case of using a sputtering method, the oxide semiconductor film may be formed using a target containing SiO2 at greater than or equal to 2 wt % and less than or equal to 10 wt %.
As another example of the In—Ga—Zn—O-based oxide semiconductor target for film formation, an oxide semiconductor target for film formation containing In, Ga, and Zn (the composition ratio of In7O3:Ga2O3:ZnO=1:1:1 (molar ratio)) or the like can be used. As the oxide semiconductor target for film formation containing In, Ga, and Zn, a target having a composition ratio of In2O3:Ga2O3:ZnO=1:1:2 (molar ratio) or a target having a composition ratio of In2O3:Ga2O3:ZnO=1:1:4 (molar ratio) can also be used. The filling rate of the oxide semiconductor target for film formation is greater than or equal to 90% and less than or equal to 100%, preferably greater than or equal to 95% and less than or equal to 99.9%. With the use of the oxide semiconductor target for film formation with a high filling factor, a dense oxide semiconductor film is formed.
The oxide semiconductor film is formed over the substrate 101 in such a manner that the substrate is held in the treatment chamber kept at reduced pressure, a sputtering gas from which hydrogen and moisture have been removed is introduced into the treatment chamber while moisture remaining therein is removed, and the above-described target is used. In order to remove moisture remaining in the treatment chamber, an entrapment vacuum pump is preferably used. For example, a cryopump, an ion pump, or a titanium sublimation pump is preferably used. Further, an evacuation unit may be a turbo pump provided with a cold trap. From the treatment chamber evacuated with a cryopump, for example, a hydrogen atom, a compound containing a hydrogen atom such as water (H2O) (preferably also a compound containing a carbon atom), and the like are removed; thus, the concentration of impurities in the oxide semiconductor film formed in the treatment chamber can be reduced. The substrate may be heated when the oxide semiconductor film is formed.
As an example of the film formation conditions, the following conditions are employed: the temperature is room temperature, the distance between the substrate and the target is 60 mm, the pressure is 0.4 Pa, the direct-current (DC) electric power is 0.5 kW, and the atmosphere is an atmosphere containing oxygen and argon (the flow rate of oxygen is 15 sccm and the flow rate of argon is 30 sccm). A pulsed direct-current (DC) power source is preferably used, in which case powder substances (also referred to as particles or dust) can be reduced and the film thickness can be uniform.
Next, in a first photolithography step, the oxide semiconductor film is processed into the island-shaped oxide semiconductor layer 107. A resist mask for forming the island-shaped oxide semiconductor layer 107 may be formed by an ink-jet method. Formation of the resist mask by an ink-jet method needs no photomask; thus, the manufacturing cost can be reduced.
Note that the etching of the oxide semiconductor film may be dry etching, wet etching, or both dry etching and wet etching.
As an etching gas for dry etching, a gas containing chlorine (chlorine-based gas such as chlorine (Cl2), boron trichloride (BCl3), silicon tetrachloride (SiCl4), or carbon tetrachloride (CCl4)) is preferably used.
Alternatively, a gas containing fluorine (fluorine-based gas such as carbon tetrafluoride (CEO, sulfur hexafluoride (SF6), nitrogen trifluoride (NF3), or trifluoromethane (CHF3)), hydrogen bromide (HBr), oxygen (O2), any of these gases to which a rare gas such as helium (He) or argon (Ar) is added, or the like can be used.
As the dry etching method, a parallel plate RIE (reactive ion etching) method or an ICP (inductively coupled plasma) etching method can be used.
As an etchant used for wet etching, a mixed solution of phosphoric acid, acetic acid, and nitric acid, or the like can be used. Alternatively, ITO07N (produced by KANTO CHEMICAL CO., INC.) may be used.
The etchant used in the wet etching is removed together with the etched materials by cleaning. The waste liquid containing the etchant and the material etched off may be purified and the material may be reused. A material such as indium contained in the oxide semiconductor layer is collected from the waste liquid after the etching and is reused, so that the resources can be efficiently used and the cost can be reduced.
The etching conditions (such as an etchant, etching time, and temperature) are adjusted as appropriate depending on the material so that the oxide semiconductor film can be etched into a desired shape.
In this embodiment, the oxide semiconductor film is processed into the island-shaped oxide semiconductor layer 107 by a wet etching method with the use of a mixed solution of phosphoric acid, acetic acid, and nitric acid as an etchant.
In this embodiment, first heat treatment is performed on the oxide semiconductor layer 107. The temperature of the first heat treatment is higher than or equal to 300° C. and lower than or equal to 800° C., preferably higher than or equal to 400° C. and lower than or equal to 700° C. Here, the substrate is put in an electric furnace that is a kind of heat treatment apparatus and heat treatment is performed on the oxide semiconductor layer 107 at 450° C. in a nitrogen atmosphere for one hour, and then water and hydrogen are prevented from entering the oxide semiconductor layer with the oxide semiconductor layer not exposed to air; thus, the oxide semiconductor layer 107 is obtained. Through the first heat treatment, the oxide semiconductor layer 107 can be dehydrated or dehydrogenated.
Note that the heat treatment apparatus is not limited to an electric furnace, and may have a device for heating an object by heat conduction or heat radiation from a heating element such as a resistance heating element. For example, an RTA (rapid thermal anneal) apparatus such as a GRTA (gas rapid thermal anneal) apparatus or an LRTA (lamp rapid thermal anneal) apparatus can be used. An LRTA apparatus is an apparatus for heating an object to be processed by radiation of light (an electromagnetic wave) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or a high pressure mercury lamp. A GRTA apparatus is an apparatus for heat treatment using a high-temperature gas. As the gas, an inert gas which does not react with an object to be processed by heat treatment, like nitrogen or a rare gas such as argon, is used.
For example, as the first heat treatment, GRTA may be performed as follows: the substrate is transferred into an inert gas heated to a temperature as high as 650° C. to 700° C., heated for several minutes, and transferred and taken out of the inert gas heated to the high temperature. GRTA enables high-temperature heat treatment in a short time.
Note that in the first heat treatment, it is preferable that water, hydrogen, and the like be not contained in nitrogen or a rare gas such as helium, neon, or argon. Alternatively, the purity of nitrogen or a rare gas such as helium, neon, or argon which is introduced into the heat treatment apparatus is preferably greater than or equal to 6 N (99.9999%), more preferably greater than or equal to 7 N (99.99999%) (i.e., the impurity concentration is preferably lower than or equal to 1 ppm, more preferably lower than or equal to 0.1 ppm).
The first heat treatment for the oxide semiconductor layer can be performed before the oxide semiconductor film is processed into the island-shaped oxide semiconductor layer. In that case, the substrate is taken out of the heating apparatus after the first heat treatment, and then a photolithography step is performed.
The heat treatment which has an effect of dehydrating or dehydrogenating the oxide semiconductor layer may be performed at any of the following timings: after the oxide semiconductor layer is formed; after a source electrode layer and a drain electrode layer are formed over the oxide semiconductor layer; after a film which serves as sidewalls is provided for the source electrode layer and the drain electrode layer; and after a gate insulating layer is formed over the source electrode layer and the drain electrode layer.
However, as long as a purified oxide semiconductor layer in which hydrogen and water are sufficiently reduced at the time of the formation can be obtained, the first heat treatment is not necessarily performed. In the case where the purified oxide semiconductor layer in which the hydrogen concentration is sufficiently reduced at the time of the formation is formed, the substrate is held in a treatment chamber kept at reduced pressure and the substrate is heated to a temperature higher than or equal to room temperature and lower than 400° C. Then, a sputtering gas from which hydrogen and moisture have been removed is introduced into the treatment chamber while moisture remaining therein is removed, and metal oxide is used as a target. In the above-described manner, the oxide semiconductor layer is formed over the substrate. From the treatment chamber evacuated with a cryopump, for example, a hydrogen atom, a compound containing a hydrogen atom such as water (H2O) (preferably also a compound containing a carbon atom), and the like are removed; thus, the concentration of impurities in the oxide semiconductor layer formed in the treatment chamber can be reduced. When sputtering film formation is performed while moisture remaining in the treatment chamber is removed using a cryopump, the substrate temperature in forming the oxide semiconductor layer can be in the range of room temperature to a temperature lower than 400° C.
Next, a conductive film is formed over the second insulating layer 105 and the oxide semiconductor layer 107. The conductive film may be formed by a sputtering method or a vacuum evaporation method. As examples of the material for the conductive film, an element selected from Al, Cr, Cu, Ta, Ti, Mo, or W; an alloy containing any of these elements as a component; an alloy film containing any of these elements in combination; and the like can be given. Further, one or more materials selected from manganese, magnesium, zirconium, and beryllium may be used. Further, the metal conductive film may have a single-layer structure or a stacked-layer structure of two or more layers. For example, a single-layer structure of an aluminum film containing silicon; a two-layer structure of an aluminum film and a titanium film stacked thereover; a three-layer structure of a titanium film, an aluminum film stacked thereover, and a titanium film stacked thereover; and the like can be given. Alternatively, a film, an alloy film, or a nitride film of a combination of Al and one or more elements selected from titanium (Ti), tantalum (Ta), tungsten (W), molybdenum (Mo), chromium (Cr), neodymium (Nd), and scandium (Sc). In this embodiment, a stacked film of a titanium film (with a thickness of greater than or equal to 10 nm and less than or equal to 100 nm), an aluminum film (with a thickness of greater than or equal to 20 nm and less than or equal to 500 nm), and a titanium film (with a thickness of greater than or equal to 10 nm and less than or equal to 100 nm) is formed as the conductive film.
Next, in a second photolithography step, a resist mask is formed over the conductive film and the conductive film is selectively etched, so that the source electrode layer 109a and the drain electrode layer 109b are formed (
Note that in order to prevent the oxide semiconductor layer 107 from being removed and the second insulating layer 105 therebelow from being exposed at the time of the etching of the conductive film, materials and etching conditions are adjusted as appropriate.
In this embodiment, In—Ga—Zn—O-based oxide can be used for the oxide semiconductor layer 107, and organic acid such as citric acid or oxalic acid, ITO07N (produced by KANTO CHEMICAL CO., INC.), or the like can be used for an etchant.
Note that, in the second photolithography step, part of the oxide semiconductor layer 107 is also etched in some cases, so that an oxide semiconductor layer having a groove (a depressed portion) might be formed. The resist mask for forming the source electrode layer 109a and the drain electrode layer 109b may be formed by an ink-jet method. Formation of the resist mask by an ink-jet method needs no photomask; thus, the manufacturing cost can be reduced.
Ultraviolet light, KIT laser light, or ArF laser light is used for light exposure for forming the resist mask in the second photolithography step.
Next, an insulating layer 120 is formed over the oxide semiconductor layer 107, the source electrode layer 109a, and the drain electrode layer 109b (
As the insulating layer 120, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, a silicon nitride oxide film, a titanium oxide film, an aluminum oxide film, or the like is formed by a sputtering method.
Next, most of the insulating layer 120 is removed by overall etching, so that the sidewalls 121 which are in contact with a top surface of the oxide semiconductor layer 107 are provided on side surfaces of the source electrode layer 109a and the drain electrode layer 109a and the top surface of the oxide semiconductor layer 107 (
The sidewall 121 may be formed using a conductive material, for example, a metal material. Specifically, a metal film is formed, instead of the insulating layer 120, over the source electrode layer 109a and the drain electrode layer 109b. The metal film can be formed using a metal material such as a metal element such as titanium, aluminum, or tungsten, an alloy containing the metal element as a component, or an alloy containing the above metal elements in combination.
Next, most of the metal film is removed by etching, so that the sidewalls 121 of the source electrode layer 109a and the drain electrode layer 109b which are in contact with the top surface of the oxide semiconductor layer 107 are formed. The sidewall 121 formed using a conductive material becomes a conductive sidewall, so that the sidewall is electrically connected to the side surface of the source electrode layer 109a or the drain electrode layer 109b. In addition, the bottom surface of the sidewall of each of the source electrode layer 109a and the drain electrode layer 109b is in contact with the oxide semiconductor layer 107 to be electrically connected thereto.
Next, the gate insulating layer 117 is formed over the source electrode layer 109a, the drain electrode layer 109b, the sidewalls 121, and the oxide semiconductor layer 107.
The gate insulating layer 117 can be formed to have a single-layer structure or a stacked-layer structure using a silicon oxide layer, a silicon nitride layer, a silicon oxynitride layer, a silicon nitride oxide layer, a hafnium oxide layer, a tantalum oxide layer, and/or an aluminum oxide layer by a sputtering method or the like. Note that the gate insulating layer 117 is preferably formed by a sputtering method so that a large amount of hydrogen can be prevented from being contained in the gate insulating layer 117. In the case where a silicon oxide film is formed by a sputtering method, a silicon target or a quartz target is used as a target and oxygen or a mixed gas of oxygen and argon is used as a sputtering gas.
The gate insulating layer 117 can have a structure in which a silicon oxide layer and a silicon nitride layer are stacked in this order over the source electrode layer 109a and the drain electrode layer 109b. For example, a gate insulating layer with a thickness of 100 nm may be formed in such a manner that a silicon oxide layer (SiOx (x>0)) with a thickness of greater than or equal to 5 nm and less than or equal to 300 nm may be formed as a first gate insulating layer and a silicon nitride layer (SiNy (y>0)) with a thickness of greater than or equal to 50 nm and less than or equal to 200 nm may be stacked as a second gate insulating layer over the first gate insulating layer by a sputtering method. In this embodiment, a silicon oxide layer with a thickness of 100 nm is formed by an RF sputtering method in an atmosphere containing oxygen and argon (the flow ratio of oxygen to argon is 1:1 (each flow rate is 25 sccm)) under conditions where the pressure is 0.4 Pa and the high-frequency electric power is 1.5 kW.
Next, a conductive film is formed over the gate insulating layer 117, and then the gate electrode layer 119 is formed in a third photolithography step. Note that a resist mask may be formed by an ink-jet method. Formation of the resist mask by an ink-jet method needs no photomask; thus, the manufacturing cost can be reduced.
The gate electrode layer 119 can be formed to have a single-layer structure or a stacked-layer structure using a metal material such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, or scandium, or an alloy material which contains any of these materials as a main component.
For example, as a two-layer structure of the gate electrode layer 119, any of the following structures are preferable: a two-layer structure of an aluminum layer and a molybdenum layer stacked thereover, a two-layer structure of a copper layer and a molybdenum layer stacked thereover, a two-layer structure of a copper layer and a titanium nitride layer or a tantalum nitride layer stacked thereover, and a two-layer structure of a titanium nitride layer and a molybdenum layer. As a three-layer structure, a stacked structure of a tungsten layer or a tungsten nitride layer, a layer of an alloy of aluminum and silicon or an alloy of aluminum and titanium, and a titanium nitride layer or a titanium layer is preferable. Note that the gate electrode layer can be formed using a light-transmitting conductive film. As an example of a material for the light-transmitting conductive film, light-transmitting conductive oxide or the like can be given.
In this embodiment, a tungsten film with a thickness of 150 nm is formed as the gate electrode layer 119.
Next, second heat treatment (preferably at a temperature higher than or equal to 200° C. and lower than or equal to 400° C., for example, higher than or equal to 250° C. and lower than or equal to 350° C.) is performed in an inert gas atmosphere or an oxygen gas atmosphere. In this embodiment, the second heat treatment is performed at 250° C. in a nitrogen atmosphere for one hour. The second heat treatment may be performed after a protective insulating layer or a planarization insulating layer is formed over the transistor 200.
Further, heat treatment may be performed at a temperature higher than or equal to 100° C. and lower than or equal to 200° C. for greater than or equal to 1 hour and less than or equal to 30 hours in the air. This heat treatment may be performed at a fixed heating temperature. Alternatively, the following change in the heating temperature may be conducted plural times repeatedly: the heating temperature is increased from room temperature to a temperature higher than or equal to 100° C. and lower than or equal to 200° C. and then decreased to room temperature. This heat treatment may be performed under reduced pressure before the formation of the oxide insulating layer. When the heat treatment is performed under reduced pressure, the heat treatment time can be shortened.
Through the above-described steps, the top-gate transistors 200 and 201 including the oxide semiconductor layers can be manufactured in each of which the sidewalls are provided for the source electrode layer and the drain electrode layer and which has a short channel length L and can be miniaturized (
A protective insulating layer or a planarization insulating layer for planarization may be provided over each of the thin film transistors 200 and 201. For example, the protective insulating layer may be formed to have a single-layer structure or a stacked-layer structure using a silicon oxide layer, a silicon nitride layer, a silicon oxynitride layer, a silicon nitride oxide layer, and/or an aluminum oxide layer.
The planarization insulating layer can be formed using an organic material having heat resistance, such as polyimide, acrylic, benzocyclobutene, polyamide, or epoxy. Other than such organic materials, it is also possible to use a low-dielectric constant material (a low-k material), a siloxane-based resin, PSG (phosphosilicate glass), BPSG (borophosphosilicate glass), or the like. Note that the planarization insulating layer may be formed by stacking a plurality of insulating layers formed using any of these materials.
There is no particular limitation on the method for forming the planarization insulating layer, and the planarization insulating layer can be formed, depending on the material, by a method such as a sputtering method, an SOG method, a spin coating method, a dip coating method, a spray coating method, or a droplet discharge method (such as an ink-jet method, screen printing, offset printing, or the like), or a tool (equipment) such as a doctor knife, a roll coater, a curtain coater, or a knife coater.
Note that the siloxane resin corresponds to a resin including a Si—O—Si bond formed using a siloxane-based material as a starting material. The siloxane-based resin may include an organic group (e.g., an alkyl group or an aryl group) or a fluoro group as a substituent. The organic group may include a fluoro group.
When both the gate insulating layer 117 and the first insulating layer 103 in the transistors 200 and 201 are formed using silicon nitride films, the oxide semiconductor layer 107 can be interposed between the silicon nitride films, whereby the entry of hydrogen or moisture can be effectively blocked. Such a structure makes it possible to reduce the concentration of water or hydrogen in the oxide semiconductor layer 107 to the minimum and to prevent the entry of water or hydrogen.
Although the transistors 200 and 201 are described as single-gate transistors, the transistors 200 and 201 can be manufactured as multi-gate transistors including a plurality of channel formation regions as necessary.
As described above, the provision of the sidewalls for the source electrode layer and the drain electrode layer makes it possible to realize a top-gate semiconductor element including an oxide semiconductor layer, which has a short channel length L and can be miniaturized. In addition, the semiconductor element of one embodiment of the present invention has a short channel length L and can be miniaturized; thus, when the semiconductor element is used in a semiconductor integrated circuit such as an LSI, a CPU, or a memory, the operation speed of the circuit is increased, and furthermore, power consumption can be reduced.
Further, in the semiconductor element of one embodiment of the present invention, the sidewalls are provided on the side surfaces of the source electrode layer and the drain electrode layer, which give tapered shapes to the source electrode layer and the drain electrode layer; thus, the coverage with the gate insulating layer can be increased and a short circuit between the gate electrode layer and the source electrode layer or the drain electrode layer can be prevented. As a result, a highly reliable semiconductor element and a highly reliable semiconductor device including the semiconductor element can be realized.
Further, a normally-off semiconductor element in which off-state current is small can be manufactured by using an oxide semiconductor layer which has a large energy gap and in which the hydrogen concentration is sufficiently reduced and the purity is increased by removal of impurities such as hydrogen and moisture. The use of the semiconductor element makes it possible to realize a semiconductor device whose power consumption due to leakage current is small.
The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.
In this embodiment, a method for manufacturing a transistor which is different from that described in the above embodiment will be described with reference to drawings. Note that the manufacturing process (a material and the like which can be used) described in this embodiment has a lot in common with that described in Embodiment 2. Therefore, in the following description, description of the same portions will not be given, and different points will be described in detail.
The transistor 300 illustrated in
An example of a method for manufacturing the transistor 300 illustrated in
First, the first insulating layer 303 is formed over the substrate 301 having an insulating surface. Then, the second insulating layer 305 is formed over the first insulating layer 303. Then, an oxide semiconductor film with a thickness of greater than or equal to 3 nm and less than or equal to 50 nm, preferably greater than or equal to 3 nm and less than or equal to 30 nm, is formed over the second insulating layer 305, and the oxide semiconductor film is processed into the island-shaped oxide semiconductor layer 307 in a first photolithography step. In this embodiment, first heat treatment is performed on the oxide semiconductor layer 307.
Next, a first conductive film 306 and a second conductive film 308 are formed over the second insulating layer 305 and the oxide semiconductor layer 307. The first conductive film 306 and the second conductive film 308 can be formed to have a single-layer structure or a stacked-layer structure using a material which is the same as that for the source electrode layer 109a and the drain electrode layer 109b described in Embodiment 2.
In this embodiment, a stacked film of a titanium film (with a thickness of greater than or equal to 10 nm and less than or equal to 100 nm) and a tungsten film (with a thickness of greater than or equal to 10 nm and less than or equal to 100 nm) thereover is formed as the first conductive film 306, and a stacked film of an aluminum film (with a thickness of greater than or equal to 20 nm and less than or equal to 500 nm) and a titanium film (with a thickness of greater than or equal to 10 nm and less than or equal to 100 nm) thereover is formed as the second conductive film 308. When a material which is not likely to transmit a substance which contaminates an oxide semiconductor (specifically hydrogen or the like) is used for the first conductive film 306, the conductive film 306 serves as a barrier film. For example, when the first conductive film 306 is formed using a tungsten film which is not likely to transmit hydrogen, the second conductive film 308 and an insulating layer 320 which serves as a sidewall can be formed by a deposition method which might contaminate the oxide semiconductor layer 307 (specifically a CVD method).
Next, an insulating layer 310 with a thickness of greater than or equal to 200 nm and less than or equal to 2000 nm is formed over the second conductive film 308 by a plasma CVD method, a sputtering method, or the like, as a single layer or a stacked layer using a silicon oxide layer, a silicon nitride layer, a silicon oxynitride layer, and/or a silicon nitride oxide layer (
There is no particular limitation on the method for forming the insulating layer, and the insulating layer can be formed, depending on the material, by a method such as a sputtering method, an SOG method, a spin coating method, a dip coating method, a spray coating method, or a droplet discharge method (such as an ink-jet method, screen printing, offset printing, or the like), or a tool (equipment) such as a doctor knife, a roll coater, a curtain coater, or a knife coater.
Next, in a second photolithography step, a resist mask is formed over the insulating layer 310 and selective etching is performed, so that the second source electrode layer 311a, the second drain electrode layer 311b, and the third insulating layer 315 are formed (
The third insulating layer 315 is provided in order to reduce parasitic capacitance between, the gate electrode layer 319 formed later and the second source electrode layer 311a or the second drain electrode layer 311b. Meanwhile, when the third insulating layer 315 is provided, in order that the second source electrode layer 311a and the second drain electrode layer 311b have tapered shapes, etching conditions such as a selectivity ratio of the third insulating layer 315 to the second source electrode layer 311a or the second drain electrode layer 311b need to be controlled, which makes processing by etching difficult. Unless the second source electrode layer 311a and the second drain electrode layer 311b are tapered, a problem arises in that the coverage with the gate insulating layer 317 stacked thereover is reduced. However, in the transistor according to one embodiment of the present invention, the sidewalls 321 are provided on side surfaces of the second source electrode layer 311a and the second drain electrode layer 311b, which give tapered shapes to the source electrode layer 311a and the drain electrode layer 311b; thus, the edges of the second source electrode layer 311a and the second drain electrode layer 311b do not need to be processed to have tapered shapes. Accordingly, the transistor can be easily manufactured.
Next, the insulating layer 320 is formed over the first conductive film 306, the second source electrode layer 311a, the second drain electrode layer 311b, and the third insulating layer 315 (
As the insulating layer 320, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, a silicon nitride oxide film, a titanium oxide film, an aluminum oxide film, or the like can be formed by a sputtering method. A metal film may be used instead of the insulating layer 320. In the case where the first conductive film 306 is formed using a material which is not likely to transmit a substance which contaminates an oxide semiconductor (specifically hydrogen or the like), the insulating layer 320 may be formed by a CVD method. The insulating layer 320 which serves as a sidewall is preferably formed by a CVD method, in which case the insulating layer 320 can be formed to have a uniform thickness.
Next, most of the insulating layer 320 is removed by overall etching, so that the sidewalls 321 are formed on side surfaces of the second source electrode layer 311a and the second drain electrode layer 311b. At this time, bottom surfaces of the sidewalls 321 are in contact with a top surface of the first conductive film 306 (
Next, the first conductive film 306 is etched using the third insulating layer 315 and the sidewalls 321 as hard masks, so that the first source electrode layer 309a and the first drain electrode layer 309b are formed (
Next, the gate insulating layer 317 is formed over the third insulating layer 315, the sidewalls 321, the first source electrode layer 309a, the first drain electrode layer 309b, and the oxide semiconductor layer 307. Then, a conductive film is formed over the gate insulating layer 317, and after that the gate electrode layer 319 is formed in a third photolithography step.
Next, second heat treatment (preferably at a temperature higher than or equal to 200° C. and lower than or equal to 400° C., for example, higher than or equal to 250° C. and lower than or equal to 350° C.) is performed in an inert gas atmosphere or an oxygen gas atmosphere. Through the above-described steps, the transistor 300 including the sidewalls on the source electrode layer and the drain electrode layer can be manufactured (
As described above, the sidewalls are provided for the source electrode layer and the drain electrode layer in the semiconductor element of one embodiment of the present invention, whereby a top-gate semiconductor element including an oxide semiconductor layer, which has a short channel length L and can be miniaturized can be realized.
Further, the semiconductor element of one embodiment of the present invention has a short channel length L and can be miniaturized; thus, when the semiconductor element is used in a semiconductor integrated circuit such as an LSI, a CPU, or a memory, the operation speed of the circuit is increased, and furthermore, power consumption can be reduced.
Further, in the semiconductor element of one embodiment of the present invention, the sidewalls are provided on the side surfaces of the source electrode layer and the drain electrode layer, which give tapered shapes to the source electrode layer and the drain electrode layer; thus, the coverage with the gate insulating layer can be increased and a short circuit between the gate electrode layer and the source electrode layer or the drain electrode layer can be prevented. As a result, a highly reliable semiconductor element and a highly reliable semiconductor device including the semiconductor element can be realized.
Further, in the semiconductor element of one embodiment of the present invention, the oxide semiconductor layer which has a large energy gap and in which the hydrogen concentration is sufficiently reduced and the purity is increased by removal of impurities such as hydrogen and moisture is used, whereby a normally-off semiconductor element in which off-state current is small can be manufactured. The use of the semiconductor element makes it possible to realize a semiconductor device whose power consumption due to leakage current is small.
The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.
In this embodiment, an example in which an inverter circuit of an integrated circuit is formed using two n-channel transistors will be described. A manufacturing process of the transistor is almost the same as that in Embodiment 2; therefore, only different portions will be described in detail.
The integrated circuit is formed using an inverter circuit, a capacitor, a resistor, and the like; therefore, a process of forming a capacitor and two kinds of resistors over the same substrate in addition to the inverter circuit will also be described.
In the case where the inverter circuit includes a combination of two n-channel transistors, the following are given as examples of the inverter circuit: an EDMOS circuit including a combination of an enhancement mode transistor and a depletion mode transistor and an EEMOS circuit including a combination of two enhancement mode transistors.
In this embodiment, an example of an EDMOS circuit will be described.
In
Voltage is applied to the electrode layer 412b and the threshold voltage is set to be negative, whereby the second transistor 401 functions as a depletion mode transistor. The electrode layer 412c is one electrode included in the capacitor. The electrode layer 412d is one electrode connected to a first resistor. The electrode layer 412e is one electrode connected to a second resistor.
In addition, a first insulating layer 413 and a second insulating layer 415 for covering the electrode layers 412b, 412c, 412d, and 412e are formed. In a capacitor portion, parts of the first insulating layer 413 and the second insulating layer 415, which overlap with the electrode layer 412c serve as dielectrics.
A second oxide semiconductor layer 417b may be thicker than a first oxide semiconductor layer 417a. Deposition and patterning are each performed twice in order to make the thickness of the second oxide semiconductor layer 417b larger than that of the first oxide semiconductor layer 417a. The thickness of the second oxide semiconductor layer 417b is increased, whereby the second transistor 401 can function as a depletion mode transistor, and voltage to make the threshold voltage negative does not need to be applied to the electrode layer 412b; thus, the electrode layer 412b can be omitted.
A third oxide semiconductor layer 417c functions as the first resistor. An opening is formed in parts of the first insulating layer 413 and the second insulating layer 415, which overlap with the electrode layer 412d, and the third oxide semiconductor layer 417c and the electrode layer 412d are electrically connected to each other through the opening. Further, a fourth oxide semiconductor layer 417d functions as the second resistor. An opening is formed in parts of the first insulating layer 413 and the second insulating layer 415, which overlap with the electrode layer 412e, and the fourth oxide semiconductor layer 417d and the electrode layer 412e are electrically connected to each other through the opening.
The fourth oxide semiconductor layer 417d may be thicker than the third oxide semiconductor layer 417c. When the third oxide semiconductor layer 417c and the fourth oxide semiconductor layer 417d have different thicknesses, the value of the resistivity of the first resistor can be different from that of the second resistor.
The first transistor 400 includes a first gate electrode layer 419a and the first oxide semiconductor layer 417a which overlaps with the first gate electrode layer 419a with a gate insulating layer 427 interposed therebetween. A first electrode layer 422a which is in contact with part of the first oxide semiconductor layer 417a is electrically connected to a first wiring 429a. The first wiring 429a is a power supply line to which negative voltage VDL is applied (a negative power supply line). This power supply line may be a power supply line with a ground potential (a ground potential power supply line).
In this embodiment, the first electrode layer 422a includes three layers and is formed using a material which is the same as that for the source electrode layer 109a and the drain electrode layer 109b in Embodiment 2. In this embodiment, after conductive films are patterned, an insulating film is formed (see
In the capacitor portion, a fourth electrode layer 422d which is a capacitor electrode layer is formed in a step and with a material which are the same as those of the first electrode layer 422a. The fourth electrode layer 422d overlaps with the electrode layer 412c.
A fifth electrode layer 422e is formed on and in contact with the fourth oxide semiconductor layer 417d which is the second resistor, in a step and with a material which are the same as those of the first electrode layer 422a.
Further, the first transistor 400 includes sidewalls 421 of the first electrode layer 422a and the second electrode layer 422b. Bottom surfaces of the sidewalls 421 are in contact with a top surface of the first oxide semiconductor layer 417a. Similarly, the second transistor 401 includes sidewalls 431 of the second electrode layer 422b and the third electrode layer 422c. Bottom surfaces of the sidewalls 431 are in contact with a top surface of the second oxide semiconductor layer 417b. The provision of the sidewalls makes it possible to manufacture a minute transistor which has a short channel length L; thus, the operation speed of a circuit can be increased, and furthermore, power consumption can be reduced.
The second transistor 401 includes the second gate electrode layer 419b which functions as a second wiring and the second oxide semiconductor layer 417b which overlaps with the second gate electrode layer 4196 with the gate insulating layer 427 interposed therebetween. A third wiring 429b is a power supply line to which positive voltage VDH is applied (a positive power supply line).
In addition, the second transistor 401 includes the second electrode layer 422b and the third electrode layer 422c which are partly in contact with and overlap with the second oxide semiconductor layer 417b. Note that the second electrode layer 422b and the third electrode layer 422c are formed in a step and with a material which are the same as those of the first electrode layer 422a.
An opening reaching the second electrode layer 422b is formed in the third insulating layer 416 and the gate insulating layer 427. The second electrode layer 422b is electrically connected to the second gate electrode layer 419b which functions as a second wiring, whereby the first transistor 400 and the second transistor 401 are connected to form an EDMOS circuit.
A fourth wiring 429c which is connected to the fourth electrode layer 422d through an opening formed in parts of the third insulating layer 416 and the gate insulating layer 427, which overlap with the electrode layer 412c functions as a capacitor wiring.
A fifth wiring 429d is in contact with the third oxide semiconductor layer 417c which functions as the first resistor through an opening formed in parts of the third insulating layer 416 and the gate insulating layer 427, which overlap with the electrode layer 412d.
In this embodiment, the example in which the EDMOS circuit, the capacitor portion, the first resistor, and the second resistor are formed over one substrate with the use of the transistor described in Embodiment 2 is described; however, the present invention is not particularly limited thereto, and the transistor described in Embodiment 3 can also be formed over the same substrate.
In
Further, the sixth electrode layer 422f can be formed with a material and in a step which are the same as those of the first electrode layer 422a. In addition, the conductive layer 439 can be formed with a material and in a step which are the same as those of the first gate electrode layer 419a and the second gate electrode layer 419b.
This embodiment can be freely combined with any of other embodiments.
In this embodiment, an example of manufacturing a CPU (central processing unit) using the EDMOS circuit described in Embodiment 4 will be described.
These circuits are manufactured using any of the transistors, the inverter circuit, the resistor, the capacitor, and the like described in Embodiments 1 to 4. The transistors described in Embodiments 1 to 4 each include an oxide semiconductor layer which has a large energy gap and in which the hydrogen concentration is sufficiently reduced; thus, the transistors can be normally-off transistors with extremely small off-state current. In addition, in each of the transistors described in Embodiments 1 to 4, the sidewalls are provided for the source electrode layer and the drain electrode layer; thus, the transistor has a short channel length L and can be miniaturized, and the operation speed of the circuit can be increased. Thus, at least part of the CPU 1001 is formed using the transistor of one embodiment of the present invention, whereby low power consumption can be realized.
Here, each circuit is briefly described. The timing control circuit 1002 receives instructions from the outside, converts them into information for the inside, and transmits the information to another block. In addition, the timing control circuit 1002 gives directions such as reading and writing of memory data to the outside, according to internal operation. The instruction decoder 1003 has a function of converting instructions from the outside into information for the inside. The register array 1004 is a volatile memory for temporarily storing data. The address logic and buffer circuit 1005 is a circuit for specifying the address of an external memory. The data bus interface 1006 is a circuit for taking data in and out of an external memory or a device such as a printer. The ALU 1007 is a circuit for performing an operation. The instruction register 1008 is a circuit for temporarily storing instructions. The CPU includes combination of these circuits.
This embodiment can be freely combined with any of other embodiments.
In this embodiment, an example of usage of the semiconductor device described in the above embodiment will be described. Specifically, application examples of a semiconductor device capable of inputting and outputting data without contact will be described below with reference to drawings. The semiconductor device capable of inputting and outputting data without contact is also referred to as an RFID tag, an ID tag, an IC tag, an RF tag, a wireless tag, an electronic tag, or a wireless chip, depending on the usage.
An example of a top structure of a semiconductor device described in this embodiment will be described with reference to
Note that a conductive shield is provided on a surface of the semiconductor integrated circuit chip 500 in order to prevent electrostatic breakdown of the semiconductor integrated circuit (e.g., malfunction of the circuit or damage to a semiconductor element) due to electrostatic discharge. In the case where the conductive shield has high resistance and current cannot pass through the pattern of the antenna 505, the antenna 505 and the conductive shield provided on the surface of the semiconductor integrated circuit chip 500 may be provided in contact with each other.
A semiconductor integrated circuit provided in the semiconductor integrated circuit chip 500 includes a plurality of elements such as transistors for constituting a memory portion or a logic portion. As the transistors for constituting the memory portion or the logic portion, the transistor of one embodiment of the present invention is used. As a semiconductor element in a semiconductor device according to this embodiment, not only a field-effect transistor but also a memory element including a semiconductor layer can be employed; thus, a semiconductor device which can meet functions required for various applications can be manufactured and provided.
In
In
Although the antenna 505 is a rectangular and loop-shaped antenna with one winding in the region surrounded by the dashed line 507, one embodiment of the present invention is not limited to this structure. The shape of the loop antenna is not limited to a rectangle and may be a shape with curve, for example, a circle. In addition, the number of windings is not limited to one and may be plural.
For the semiconductor device described in this embodiment, an electromagnetic induction method, an electromagnetic coupling method, or a microwave method can be employed. In the case of a microwave method, the shapes of the antenna 501 and the antenna 505 may be determined as appropriate in accordance with the wavelength of an electromagnetic wave.
In the case where a microwave method (e.g., UHF band (860 MHz band to 960 MHz band), or 2.45 GHz band) is used as the signal transmission method in the semiconductor device, the length, shape, or the like of the antenna may be determined as appropriate in consideration of the wavelength of an electromagnetic wave used for signal transmission. For example, the antenna can be formed into a linear shape (e.g., a dipole antenna) or a flat shape (e.g., a patch antenna or an antenna having a ribbon shape). Further, the shape of the antenna is not limited to a linear shape, and the antenna may have a curved shape, a serpentine curved shape, or a shape combining them in consideration of the wavelength of the electromagnetic wave.
In
Next, structures of the semiconductor integrated circuit chip 500 and the booster antenna, and arrangement thereof will be described. The semiconductor device including the transistor of one embodiment of the present invention can be used for the semiconductor integrated circuit chip 500 illustrated in
The semiconductor integrated circuit 503 illustrated in
In
Next, operation of the semiconductor device of this embodiment will be described.
Note that the booster antenna 522 can be divided into the loop-shaped portion which is mainly electromagnetically coupled to the on-chip antenna 524 and a portion which mainly receives an electric wave from the interrogator 521. The shape of the portion of the booster antenna 522 which mainly receives radio waves from the interrogator 521 is not particularly limited as long as the booster antenna 522 can receive radio waves. For example, the shape of a dipole antenna, a folded dipole antenna, a slot antenna, a meander line antenna, a microstrip antenna, or the like may be used.
Although
In the semiconductor device of this embodiment, the on-chip antenna is used and a signal or electric power can be transmitted and received between the booster antenna and the on-chip antenna without contact; therefore, unlike the case where an external antenna is connected to a semiconductor integrated circuit, the semiconductor integrated circuit and the antenna are less likely to be disconnected due to external force, and generation of initial failure in the connection can also be suppressed. In addition, since the booster antenna is used in this embodiment, unlike the case where only the on-chip antenna is used, the advantage of an external antenna can also be offered. In other words, the area of the semiconductor integrated circuit does not significantly limit the size or shape of the on-chip antenna, the frequency band of radio waves capable of being received is not limited, and the communication distance can be increased.
The semiconductor integrated circuit can be directly formed on a flexible substrate. Alternatively, the semiconductor integrated circuit may be transferred from a formation substrate (e.g., a glass substrate) to another substrate (e.g., a plastic substrate).
There is no particular limitation on the method of transferring the semiconductor integrated circuit from the formation substrate to another substrate, and a variety of methods can be used. For example, a separation layer may be formed between the formation substrate and the semiconductor integrated circuit.
For example, in the case where a metal oxide film is formed as the separation layer, the metal oxide film is weakened by crystallization, and an element layer including the semiconductor integrated circuit, which is a layer to be separated, can be separated from the formation substrate. After the metal oxide film is weakened by crystallization, part of the separation layer may be removed by etching with use of a halogen fluoride gas such as NF3, BrF3, or ClF3, and then separation may be performed in the weakened metal oxide film.
Further, in the case where a substrate having a light-transmitting property is used as the formation substrate and a film containing nitrogen, oxygen, hydrogen or the like (e.g., an amorphous silicon film containing hydrogen, an alloy film containing hydrogen, an alloy film containing oxygen or the like) is used as the separation layer, the separation layer is irradiated with laser light through the formation substrate, and nitrogen, oxygen, or hydrogen contained in the separation layer is evaporated so that separation can occur between the formation substrate and the separation layer.
Alternatively, the layer to be separated may be separated from the formation substrate by removing the separation layer by etching.
Alternatively, a method of removing the formation substrate by mechanical grinding or a method of removing the formation substrate by etching using a halogen fluoride gas such as NF3, BrF3, or ClF3 or HF, or the like can be employed. In this case, the separation layer can be omitted.
Alternatively, laser irradiation, etching using a gas, a solution, or the like, or a sharp knife or a scalpel, can be used so as to form a groove to expose the separation layer. The groove can trigger separation of the layer to be separated from the formation substrate from the separation layer.
As the separation method, for example, mechanical force (separation treatment with human hands or with a gripper, separation treatment by rotation of a roller, or the like) may also be used. Alternatively, the layer to be separated may be separated from the separation layer in such a manner that liquid is dropped into the groove so that the liquid to be infiltrated into the interface between the separation layer and the layer to be separated. Alternatively, a method can be employed in which a fluoride gas such as NF3, BrF3, or ClF3 is introduced into the groove, and the separation layer is removed by etching with the use of the fluoride gas so that the layer to be separated is separated from the formation substrate. Further alternatively, the separation may be performed while pouring liquid such as water during the separation.
As another separation method, in the case where the separation layer is formed using tungsten, separation can be performed while the separation layer is etched by a mixed solution of ammonia water and hydrogen peroxide water.
As described above, by using the transistor of one embodiment of the present invention, a semiconductor device can be manufactured. The transistor of one embodiment of the present invention has a short channel length L and can be miniaturized; thus, the operation speed of the circuit can be increased, and furthermore, power consumption of the semiconductor device can be reduced.
This embodiment can be freely combined with any of other embodiments.
In this embodiment, application examples of a semiconductor device capable of inputting and outputting data without contact which is formed using the device described in Embodiment 6 will be described with reference to drawings. The semiconductor device capable of inputting and outputting data without contact is also referred to as an RFID tag, an ID tag, an IC tag, an IC chip, an RF tag, a wireless tag, an electronic tag, or a wireless chip, depending on the usage.
A semiconductor device 800 has a function of exchanging data without contact and includes a high-frequency circuit 810, a power supply circuit 820, a reset circuit 830, a clock generation circuit 840, a data demodulation circuit 850, a data modulation circuit 860, a control circuit 870 for controlling other circuits, a memory circuit 880, and an antenna 890 (
Next, an example of the operation of the above semiconductor device will be described. First, a radio signal is received by the antenna 890. The radio signal is transmitted to the power supply circuit 820 via the high frequency circuit 810, thereby generating high power supply potential (hereinafter referred to as a VDD). The VDD is supplied to each circuit included in the semiconductor device 800. A signal which is transmitted to the data demodulation circuit 850 via the high frequency circuit 810 is demodulated (hereinafter, the signal is referred to as a demodulated signal). Moreover, a signal passed through the reset circuit 830 and the clock generation circuit 840 via the high frequency circuit 810, and the demodulated signal are transmitted to the control circuit 870. The signals transmitted to the control circuit 870 are analyzed by the code extracting circuit 910, the code judging circuit 920, the CRC judging circuit 930, and the like. Then, on the basis of the analyzed signals, information of the semiconductor device stored in the memory circuit 880 is output. The output data of the semiconductor device is encoded via the output unit circuit 940. In addition, the encoded data of the semiconductor device 800 passes through the data modulation circuit 860 to be transmitted as a radio signal via the antenna 890. Note that low power supply potential (hereinafter referred to as VSS) is common in the plurality of circuits included in the semiconductor device 800, and GND can be used as VSS.
In this manner, the data of the semiconductor device 800 can be read by transmitting a signal from a communication device to the semiconductor device 800 and receiving a signal from the semiconductor device 800 by the communication device.
Further, the semiconductor device 800 may be one in which a power source (e.g., a battery) is not included and a power supply voltage is supplied to circuits by using electromagnetic waves. The semiconductor device 800 may also be one in which a power source (e.g., a battery) is included, and a power supply voltage is supplied to circuits by using both electromagnetic waves and the power source (battery).
Next, an example of the usage of a semiconductor device capable of inputting and outputting data without contact will be described. A side surface of a mobile terminal which includes a display portion 3210 is provided with a communication device 3200. A side surface of a product 3220 is provided with a semiconductor device 3230 (
As described above, a semiconductor device of the present invention, which has a very wide range of application, can be used in electronic devices in all kinds of fields.
In this embodiment, an example of a memory circuit which can be formed using any of the transistors described in Embodiments 1 to 4 will be described.
Each of the memory elements 1100 includes a capacitor and a transistor. One of a source and a drain of the transistor is connected to the signal line, and the other of the source and the drain of the transistor is connected to one electrode of the capacitor, and the other electrode of the capacitor is connected to the low potential side (preferably, reference potential VSS).
The writing and refresh circuit illustrated in
The signal line connected though the first switch 1104 and the second switch 1105 are connected to the sense amplifier through the third switch 1106. A signal is output to the output signal line (OUT) from the sense amplifier.
The above-described AND circuit may have a general structure, and preferably has a simple structure.
The sense amplifier is a circuit having a function of amplifying a signal which is input.
Note that as a signal here, an analog signal or a digital signal which uses, for example, voltage, current, resistance, frequency, or the like can be used. For example, at least first potential and second potential are set, that is, high-level (also referred to as high potential or VH) potential is used as the first potential and low-level (also referred to as low potential or VL) potential is used as the second potential, whereby a binary digital signal can be set. Although VH and VL are preferably constant values, VH and VL each may take a range of values, in consideration of influence of noise.
As described above, a memory circuit can be manufactured using the transistor and the capacitor described in the above embodiment.
The refresh timing of the memory circuit is set to a certain time interval in the design phase on the basis of the leakage current of the memory elements which is evaluated in advance. In other words, the refresh timing is set in consideration of the temperature dependence of leakage current and fluctuation of the manufacturing process, after the chip is completed.
In a transistor of one embodiment of the present invention, sidewalls are provided for a source electrode layer and a drain electrode layer; thus, the transistor has a short channel length L and can be miniaturized. When a circuit is formed using the transistor, low power consumption can be realized and the operation of a memory circuit can be stabilized.
A transistor of one embodiment of the present invention includes an oxide semiconductor layer which has a large energy gap and in which the hydrogen concentration is sufficiently reduced; thus, off-state current of the transistor can be extremely small and the temperature characteristics of off-state current at a temperature ranging from −30° C. to 120° C. are hardly changed and an extremely small off-state current can be maintained. Accordingly, a normally-off transistor can be realized.
Thus, by using the transistor of one embodiment of the present invention, a refresh interval can be set long compared to a transistor including silicon, and power consumption in a standby period can be reduced.
Further, since the off-state current has little temperature dependence, the memory circuit in this embodiment is suitable for an in-vehicle electronic device. Since leakage current in a standby period is extremely small, in the case of using the memory circuit in an electric vehicle, the traveling distance per certain amount of charging hardly changes in a standby period.
This embodiment can be freely combined with any of other embodiments.
In this embodiment, an example of a shift register which can be formed using any of the transistors described in the above embodiments will be described.
In the two clock signal lines, each clock signal is input as follows: when one clock signal line is switched to high level (VH), the other is switched to low level (VL).
With reference to the shift register illustrated in
The clock signal line CLK is a wiring to which a clock signal CK is input.
The clock signal line CLKB is a wiring to which a clock signal CKB is input.
The clock signal CK and the clock signal CKB can be generated using, for example, a NOT circuit (inverter circuit).
A start signal SP and a start signal SPB are input to the first flip-flop, a clock signal CK is input thereto as a clock signal, and the first flip-flop outputs an output signal OUT1 depending on the states of the signal SP, the signal SPB, and the clock signal CK, which has been input. In this specification, the state of a signal refers to, for example, potential, current, or a frequency of the signal.
The start signal SP and the start signal SPB can be generated using, for example, a NOT circuit (inverter circuit).
In this specification, as a signal, for example, an analog signal or a digital signal which uses voltage, current, resistance, frequency, or the like can be used. For example, at least first potential and second potential are set, that is, high-level (also referred to as high potential or VH) potential is used as the first potential and low-level (also referred to as low potential or VL) potential is used as the second potential, whereby a binary digital signal can be set. Although VH and VL are preferably constant values, VH and VL each may take a range of values, in consideration of influence of noise.
The second flip-flop has the following function: to the second flip-flop, the output signal OUT1 of the first flip-flop is input as a start signal SP, and a clock signal CKB is input as a clock signal, and the second flip-flop outputs a signal OUT2 as an output signal, which is set depending on the states of an output signal and the clock signal CKB which have been input.
The start signal SP is input to one of a source and a drain of a first transistor 1111 and one of a source or a drain of a fourth transistor 1114.
The start signal SPB is input to one of a source and a drain of a second transistor 1112 and one of a source or a drain of a third transistor 1113.
The clock signal CK is input to each gate of the first transistor 1111, the second transistor 1112, the third transistor 1113, and the fourth transistor 1114.
The other of the source and the drain of the first transistor 1111 is connected to a gate of a fifth transistor 1115 and one electrode of a first capacitor 1119.
The other of the source and the drain of the second transistor 1112 is connected to a gate of a sixth transistor 1116 and one electrode of a second capacitor 1120.
The other of the source and the drain of the third transistor 1113 is connected to a gate of a seventh transistor 1117 and one electrode of a third capacitor 1121.
The other of the source and the drain of the fourth transistor 1114 is connected to a gate of an eighth transistor 1118 and one electrode of a fourth capacitor 1122.
A drain of the fifth transistor 1115 is connected to the high potential side (preferably, power supply potential Vdd). A source of the fifth transistor 1115 is connected to the other electrode of the first capacitor 1119 and a drain of the sixth transistor 1116, and outputs an output signal OUT. The other electrode of the second capacitor 1120 and a source of the sixth transistor 1116 are connected to the low potential side (preferably, reference potential VSS).
A drain of the seventh transistor 1117 is connected to the high potential side (preferably, power supply potential Vdd). A source of the seventh transistor 1117 is connected to the other electrode of the third capacitor 1121 and a drain of the eighth transistor 1118, and outputs an output signal OUTB. The other electrode of the fourth capacitor 1122 and a source of the eighth transistor 1118 are connected to the low potential side (preferably, reference potential Vss).
The first capacitor 1119, the second capacitor 1120, the third capacitor 1121, and the fourth capacitor 1122 can be formed over the same substrate as the transistor, using the capacitor described in the above embodiment.
As described above, the flip-flop circuit can be manufactured using the transistor of one embodiment of the present invention, which includes a purified oxide semiconductor layer. The transistor of one embodiment of the present invention in which sidewalls are provided for a source electrode layer and a drain electrode layer has a short channel length L and can be miniaturized; thus, the operation speed of a circuit can be increased and power consumption can be reduced.
This embodiment can be freely combined with any of other embodiments.
In this embodiment, an example of a booster circuit (a charge pump circuit) which can be formed using any of the transistors described in the above embodiments will be described.
Note that a clock signal line may be further provided.
A transistor and a capacitor may be additionally provided in accordance with the potential to be output.
In the two clock signal lines, each clock signal is input as follows: when one clock signal line is switched to high level (VH), the other is switched to low level (VL).
The clock signal CK and the clock signal CKB can be generated using, for example, a NOT circuit (an inverter circuit). The NOT circuit can be manufactured using the EDMOS circuit described in Embodiment 4.
By using the booster circuit illustrated in
Note that here, the fixed potential at which the other electrode of the storage capacitor is held may be, for example, power supply potential Vdd or reference potential Vss.
In this specification, as a signal, for example, an analog signal or a digital signal which uses voltage, current, resistance, frequency, or the like can be used. For example, at first potential and second potential are set, that is, high-level (also referred to as high potential or VH) potential is used as the first potential and low-level (also referred to as low potential or VL) potential is used as the second potential, whereby a binary digital signal can be set. Although VH and VL are preferably constant values, VH and VL each may take a range of values, in consideration of influence of noise.
As described above, the booster circuit can be manufactured using any of the transistors described in the above embodiments. The transistor of one embodiment of the present invention, in which sidewalls are provided for a source electrode layer and a drain electrode layer, has a short channel length L and can be miniaturized; thus, the operation speed of a circuit can be increased and power consumption can be reduced.
This embodiment can be freely combined with any of other embodiments.
In this embodiment, examples of electronic devices each of which is mounted with a semiconductor integrated circuit which can be obtained according to any of Embodiments 1 to 10 will be described with reference to
A semiconductor integrated circuit including any of the transistors described in the above embodiments is mounted on a motherboard. A semiconductor integrated circuit is manufactured by mounting a logic circuit, a flash memory circuit, an SRAM circuit, a DRAM circuit, and the like. Further, the CPU described in the above embodiment or a logic circuit can be mounted as well. The semiconductor integrated circuit can be mounted by a wire bonding method. In that case also, integrated circuit films having various shapes can be mounted.
Further, an FPC is attached to the circuit board, and the circuit board is connected to a display device or the like through the FPC. A driver and a controller of a display portion can be formed. The driver of the display portion includes the shift register or the EDMOS circuit described in the above embodiment.
A display portion 2705 and a display portion 2707 are incorporated in the housing 2701 and the housing 2703, respectively. The display portion 2705 and the display portion 2707 may display one image or different images. In the case where the display portion 2705 and the display portion 2707 display different images, for example, a display portion on the right side (the display portion 2705 in
The e-book reader 2700 may have a configuration capable of wirelessly transmitting and receiving data. Through wireless communication, desired book data or the like can be purchased and downloaded from an ebook server.
Further, the display panel 2802 is provided with a touch panel. A plurality of operation keys 2805 which is displayed as images is indicated by the dashed line in
Further, in addition to the above structure, the contactless IC chip described in the above embodiment or a small memory device, or the like may be incorporated.
In the display panel 2802, the direction of display is changed as appropriate depending on the usage pattern. Further, the display device is provided with the camera lens 2807 on the same surface as the display panel 2802; thus, it can be used as a video phone. The speaker 2803 and the microphone 2804 can be used for videophone, recording, playback, and the like without being limited to verbal communication. Moreover, the housings 2800 and 2801 in a state where they are developed as illustrated in
The external connection terminal 2808 can be connected to an AC adapter and various types of cables such as a USB cable, and charging and data communication with a personal computer are possible. Moreover, a large amount of data can be stored by inserting a storage medium into the external memory slot 2811 and can be moved.
Further, in addition to the above functions, an infrared communication function, a television reception function, or the like may be provided.
As described above, a semiconductor device including the transistor described in the above embodiment has a very wide range of application, and can be used in electronic devices in all kinds of fields. The transistor of one embodiment of the present invention, in which sidewalls are provided for a source electrode layer and a drain electrode layer, has a short channel length L and can be miniaturized. Thus, by using the transistor of one embodiment of the present invention, the operation speed of a circuit can be increased and power consumption of an electronic device can be reduced.
This embodiment can be freely combined with any one of Embodiments 1 to 10.
This application is based on Japanese Patent Application serial no. 2009-276004 filed with Japan Patent Office on Dec. 4, 2009, the entire contents of which are hereby incorporated by reference.
101: substrate, 102: electrode layer, 103: first insulating layer, 105: second insulating layer, 107: oxide semiconductor layer, 109a: source electrode layer, 109b: drain electrode layer, 117: gate insulating layer, 119: gate electrode layer, 120: insulating layer, 121: sidewall, 199: dashed line portion, 200: transistor, 201: transistor, 300: transistor, 301: substrate, 303: first insulating layer, 305: second insulating layer, 306: conductive film, 307: oxide semiconductor layer, 308: conductive film, 309a: first source electrode layer, 309b: first drain electrode layer, 310: insulating layer, 311a: second source electrode layer, 311b: second drain electrode layer, 315: third insulating layer, 317: gate insulating layer, 319: gate electrode layer, 320: insulating layer, 321: sidewall, 400: first transistor, 401: second transistor, 411: substrate, 412b: electrode layer, 412c: electrode layer, 412d: electrode layer, 412e: electrode layer, 412f: electrode layer, 413: first insulating layer, 415: second insulating layer, 416: third insulating layer, 417a: first oxide semiconductor layer, 417b: second oxide semiconductor layer, 417c: third oxide semiconductor layer, 417d: fourth oxide semiconductor layer, 419a: first gate electrode layer, 419b: second gate electrode layer, 421: sidewall, 422a: first electrode layer, 422b: second electrode layer, 422c: third electrode layer, 422d: fourth electrode layer, 422e: fifth electrode layer, 422f: sixth electrode layer, 427: gate insulating layer, 429a: first wiring, 429b: third wiring, 429c: fourth wiring, 429d: fifth wiring, 431: sidewall, 439: conductive layer, 500: semiconductor integrated circuit chip, 501: antenna, 502: insulator, 503: semiconductor integrated circuit, 505: antenna, 506: supporting substrate, 507: dashed line, 508: feeding point, 510: insulating layer, 512: insulator, 520: semiconductor device, 521: interrogator, 522: antenna, 523: semiconductor integrated circuit, 524: antenna, 800: semiconductor device, 810: high-frequency circuit, 820: power supply circuit, 830: reset circuit, 840: clock generation circuit, 850: data demodulation circuit, 860: data modulation circuit, 870: control circuit, 880: memory circuit, 890: antenna, 910: code extraction circuit, 920: code determination circuit, 930: CRC determination circuit, 940: output unit circuit, 1001: CPU, 1002: timing control circuit, 1003: instruction decoder, 1004: register array, 1005: address logic and buffer circuit, 1006: data bus interface, 1007: ALU, 1008: instruction register, 1100: memory element, 1101: first logic integrated circuit, 1102: second logic integrated circuit, 1103: third logic integrated circuit, 1104: first switch, 1105: second switch, 1106: third switch, 1111: first transistor, 1112: second transistor, 1113: third transistor, 1114: fourth transistor, 1115: fifth transistor, 1116: sixth transistor, 1117: seventh transistor, 1118: eighth transistor, 1119: first capacitor, 1120: second capacitor, 1121: third capacitor, 1122: fourth capacitor, 1123: transistor, 1124: capacitor, 2700: e-book reader, 2701: housing, 2703: housing, 2705: display portion, 2707: display portion, 2711: hinge, 2721: power switch, 2723: operation key, 2725: speaker, 2800: housing, 2801: housing, 2802: display panel, 2803: speaker, 2804: microphone, 2805: operation key, 2806: pointing device, 2807: camera lens, 2808: external connection terminal, 2810: solar battery cell, 2811: external memory slot, 3001: main body, 3002: housing, 3003: display portion, 3004: keyboard, 3021: main body, 3022: stylus, 3023: display portion, 3024: operation button, 3025: external interface, 3051: main body, 3053: eyepiece, 3054: operation switch, 3055: display portion B, 3056: battery, 3057: display portion A, 3200: communication device, 3210: display portion, 3220: product, 3230: semiconductor device, 3240: communication device, 3250: semiconductor device, and 3260: product
Suzawa, Hideomi, Kurata, Motomu, Mikami, Mayumi
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